On a wet Saturday morning in a square in Leeds, three men stand by a trestle table preaching Islam. "We have many questions – what are we doing here, why are we created?" Hamed asks while handing out guides to the Koran to passers-by. A few yards away a man gives out vouchers offering cash for unwanted gadgets. At the centre of the square, a young plane tree emerges from a ringed, chrome bench – a commemoration of the Queen's diamond jubilee in 2012.

Competing for the attention of shoppers are five men drawn here by their appetite for a British revolution, and the uprooting of what they view as the last barrier to real democracy. They too had plans to set up a table and a banner outside St John's shopping centre but Tony, the table guy, is running late. So the core of the Yorkshire branch of Republic, Britain's only notable republican campaign group, have spread out. Armed with leaflets, they take their argument to Leeds, one shopper at a time.

By chance, one of the first people the group meets angrily distils much of what Republic is up against. "I think it's disgusting that they're giving these out," says Lyn Adkin, 58, seconds after receiving a "Royal Secrets Must End" leaflet. She shakes it as she speaks. "I'm absolutely appalled. The Royal Family symbolise England and everything about them is English and it's wonderful. To be giving things like this out, I just don't know what to say. I'm gobsmacked and this is going in the nearest bin."

First we review the bullet points on the front of the leaflet. "The monarchy is not covered by Freedom of Information rules; Prince Charles is lobbying government in secret; millions of pounds of royal costs are hidden; the monarchy is one of the most secretive institutions in the country." Does any of this concern Mrs Adkin? "We all have secrets," she says. "And look at how they promote things, how many people come to England to look at Buckingham Palace and see the Queen. They do good! I'm so sorry to be so angry. I'm so angry, I really am."

Nigel Catling, the campaigner who gave Mrs Adkin the literature as she passed, has seen but not heard the conversation. He approaches her again to offer a different "Monarchy Must Go" leaflet, not realising what he's walking into. "I really don't want it and I'm appalled at this and I think it's disgusting," she tells him. Catling, 57, cheerily tries to start a debate but soon wishes Mrs Adkin a good day. Since it started three years ago, the Yorkshire network has leafleted cities about once a fortnight. Is it always like this? "Er, no, no it's not," he says as he looks at my tape recorder. "Would you mind turning that off?"

Queen Elizabeth II: Life in pictures Show all 50 1 /50 Queen Elizabeth II: Life in pictures Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II on a walk-about in Portsmouth during her Silver Jubilee tour of Great Britain, 1977 Queen Elizabeth II: Life in pictures Queen Elizabeth II The future Britain's Queen Elizabeth II (R) pictured with her younger sister Princess Margaret (L) in 1933 AFP/Getty Images) Queen Elizabeth II: Life in pictures Queen Elizabeth II The 9-year-old Elizabeth attends an aristocratic wedding with her mother and younger sister. Later in that year with the death of her Grandfather and the Abdication of her Uncle Edward VIII she became first in line to the throne, 1936 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II The coronation of King George VI in 1937, Elizabeth aged 10 became the heir apparent to the throne Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Elizabeth and her sister arrive at Waterloo station to say goodbye to their parents as they leave to tour Canada. Elizabeth was thought too young to escort her parents on the tour and was described as "tearful" as they departed. She and her parents made the first ever transatlantic telephone call during their time away, 1939 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II The 13-year-old Elizabeth and her sister Margret address children who have been evacuated from the cities on BBC's 'The Chilrens Hour' She said "We are trying to do all we can to help our gallant sailors, soldiers and airmen, and we are trying, too, to bear our share of the danger and sadness of war. We know, every one of us, that in the end all will be well", 1940 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Just before the end of the war Elizabeth took part in training to become an ATS officer. She is pictured learning to change a tire, 1945 AFP/Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II The official announcement of Princess Elizabeth and Phillip Mountbatten's engagement. The pairing was incredibly controversial as Prince Phillip had no financial standing and he was foreign born, the prince of Denmark and Greece (though he served Britain in the war and was given British Citizenship), 1947 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II (in coach) and her husband Prince Philip, Duke of Edinburgh are cheered by the crowd after their wedding ceremony, on 20 November 1947, on their road to Buckingham Palace, London Queen Elizabeth II: Life in pictures Queen Elizabeth II Elizabeth smiles at her first child, a month old Prince Charles. Charles was born on 14 November 1948 Corbis Queen Elizabeth II: Life in pictures Queen Elizabeth II The couples second child Princess Anne was born in 1950 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Arriving back in England upon hearing the death of her father King George VI. The Kings health had been in decline for a number of years and Elizabeth had been filling in for him on an official visit to Australia by way of Kenya. As his heir Elizabeth became Queen aged 26 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth's coronation took place on 2 June 1953. It was the first ever coronation to be aired live on television, being one of the most watched events in history with millions gathering around their TV sets to see the new monarch Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II standing next to her daughter Princess Anne, 1960 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II President Eisenhower (centre) with the British Royal family (L-R) Prince Philip, Princess Anne, HM Queen Elizabeth, Prince Charles and Captain John Eisenhower, at Balmoral Castle, Scotland, 1959 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II as she turns to smile and talk to an unidentified officer, during the Trooping of the Colour by the First Battalion of the Jamaica Regiment at Up-Park Camp, Kingston, Jamaica, 1966 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II walking cross country at the North of Scotland Gun Dog Association Open Stake Retreiver Trials in the grounds of Balmoral Castle in 1967 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II during her visit to the Chelsea Flower Show in London, a regular fixture in the royal calendar, 1971 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II and the Duke of Edinburgh during their traditional summer break at Balmoral Castle. The highland retreat is one of the Queen's favourite places, each year, she heads off to Scotland for the summer. "It is rather nice to hibernate for a bit when one leads such a moveable life," she once said, 1976 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II during a walkabout in Muscat while visiting Oman, 1979 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II with some of her corgis walking the Cross Country course during the second day of the Windsor Horse Trials. The monarch is responsible for introducing a new breed of dog known as the "dorgi" when her corgi Tiny was mated with a dachshund "sausage dog" called Pipkin which belonged to Princess Margaret, 1980 Queen Elizabeth II: Life in pictures Queen Elizabeth II (L-R) the Queen Mother, Queen Elizabeth II, Prince William, Prince Harry and the Prince and Princess of Wales after the christening ceremony of Prince Harry, 1984 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II taking the salute of the Household Guards regiments during the Trooping of the Colour ceremony in London, 1985 Queen Elizabeth II: Life in pictures Queen Elizabeth II Diana, Princess of Wales and Queen Elizabeth II as they smile to well-wishers outside Clarence House in London, 1987 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II, with Chief Instructor, Small Arms Corp LT Col George Harvey, firing the last shot on a standard SA 80 rifle when she attended the centenary of the Army Rifle Association at Bisley, 1993 Queen Elizabeth II: Life in pictures Queen Elizabeth II South Africa's President Nelson Mandela greets Queen Elizabeth II as she steps from the royal yacht Britannia in Cape Town at the 1995's official start of the her first visit to the country since 1947 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II smiles as she visits Bowring Park in St. John's, Newfoundland, on the third day of a 10-day official visit to Canada, 1997 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen accompanied by the Duke of Edinburgh make their way into St. George's Chapel at Windsor for the annual Garter ceremony, 1999 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II and Pope John Paul II as they meet at the Vatican, 2000 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II and the Queen Mother leaving church by horse drawn carriage on the Sandringham Estate, Norfolk, 2000 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth rides her horse in the grounds of Windsor Castle, 2002 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth arrives for the world premiere of James Bond movie "Casino Royale" at the Odeon cinema in Leicester Square in London, 2006 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth boards a scheduled train at Kings Cross station in London, 2009 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II planting a tree at Newmarket Animal Health Trust, during a royal visit which marked her 50th year as the charity's patron, 2009 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II talking with Pope Benedict XVI during an audience in the Morning Drawing Room at the Palace of Holyroodhouse in Edinburgh during a four day visit by the Pope to the UK, 2010 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II visiting the Sheikh Zayed Mosque in Abu Dhabi, United Arab Emirates, 2010 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II receives flowers from the crowd during her visit to Federation Square in downtown Melbourne, 2011 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth watches a preview of her Christmas message wearing a pair of 3D glasses, studded with Swarovski crystals in the form of a "Q", at Buckingham Palace in central London, 2012 Queen Elizabeth II: Life in pictures Queen Elizabeth II Members of Britain's royal family (front L to R) Prince Philip, Queen Elizabeth and Prince Charles cheer as competitors participate in a sack race at the Braemar Gathering in Braemar, Scotland, 2012 Queen Elizabeth II: Life in pictures Queen Elizabeth II Britain's Prince Charles kisses the hand of his mother Queen Elizabeth at the end of her Diamond Jubilee concert in front of Buckingham Palace in London, 2012 Reuters Queen Elizabeth II: Life in pictures Queen Elizabeth II Catherine, Duchess of Cambridge laughs as Queen Elizabeth gestures during a visit to Vernon Park in Nottingham, 2012 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II and Prince Philip attend a service for the Order of the British Empire at St Paul's Cathedral in London, 2012 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II meets young people during an official visit to The Shard building in central London, 2013 Queen Elizabeth II: Life in pictures Queen Elizabeth II Actress Angelina Jolie is presented with the Insignia of an Honorary Dame Grand Cross of the Most Distinguished Order of St Michael and St George by Queen Elizabeth II in the 1844 Room at Buckingham Palace, London, 2014 Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II and Prince Philip, Duke of Edinburgh visit the Blood Swept Lands and Seas of Red evolving art installation at the Tower of London, 2014 Queen Elizabeth II: Life in pictures Queen Elizabeth II The Queen and the Duke of Edinburgh at the State Opening of Parliament, 2015 AFP/Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II (L-R) Britain's Princess Anne, Princess Royal, Camilla, Duchess of Cornwall, Prince Charles, Prince of Wales, Prince William, Duke of Cambridge holding his son Prince George of Cambridge, Catherine, Duchess of Cambridge, Queen Elizabeth II, Prince Harry (back), Prince Andrew, Duke of York (back), James, Viscount Severn (front), Princess Beatrice of York (back), Prince Philip, Duke of Edinburgh and Princess Eugenie of York (back) stand on the balcony of Buckingham Palace waiting to view the fly-past during the Queen's Birthday Parade, 'Trooping the Colour,' in London, 2015 Queen Elizabeth II: Life in pictures Queen Elizabeth II The Trooping of the Colour is an annual celebration marking the Queen's birthday, 2015 Getty Queen Elizabeth II: Life in pictures Queen Elizabeth II Britain's Queen Elizabeth II stands with Kate the Duchess of Cambridge whilst pushing Princess Charlotte in a pram as they leave after attending the Christening of Britain's Princess Charlotte at St. Mary Magdalene Church in Sandringham, 2015 AP Photo/Matt Dunham, Pool Queen Elizabeth II: Life in pictures Queen Elizabeth II Queen Elizabeth II arrives at the Broadway Theatre in Barking, 2015 Tim P. Whitby/Getty Images

It can be tough being a republican in Britain. The Queen's annus has been pretty mirabilis over and again since the horrible 1990s, when scandal, a castle fire and Diana's death shook the House of Windsor. The Duke and Duchess of Cambridge will celebrate their fifth wedding anniversary this April, rounding off a diamond era for the family. The "Jubilympics", two births and a record-breaking reign have inspired countless souvenir pullouts, commemorative crockery and Nicholas Witchell reports on the BBC. Days before the leafleting in Leeds, a nation cooed as Prince George started nursery. And we watched Charles and his sons celebrate 40 years of the Prince's Trust with Ant and Dec.

Yet republicans are confident that an underestimated, largely unheard chunk of the population – a majority, they believe – is ready to think seriously about change in the year the Queen turns 90. And Republic, which has operated in its current form for 10 years now, thinks it can achieve it without even needing to convert people like Mrs Adkin. "I think about 20 per cent of the population is republican," Tony says when he does arrive, repeating a figure that is generally reflected in polls (he asks that his surname is not revealed "for work reasons"). "I also maintain that about 20 per cent of us are monarchists. That leaves 60 per cent in the middle who don't really care. But the media try and put them in with the monarchists and it's just not the case."

Republic's mission is to find and engage shy and unwitting republicans. By reversing the trade winds of royal glorification that still make the weather here, it wants to create a climate in which a government is compelled to hold a referendum – and then to persuade us to vote for an elected head of state. With that would come an elected second chamber in place of the House of Lords. But first they want their arguments to be heard over the din of ad-libbing royal correspondents and cathedral organs. And in this regard, they, too, have had a good year.

In December, a Freedom of Information request that Republic had pursued for three years revealed the routine access to confidential government papers enjoyed by Prince Charles, the wealthy businessman, landowner, lobbyist and future unelected head of state. The revelation made front-page news only months after the release of some of the prince's "black spider" memos to ministers, which confirmed suspicions about his "meddling" tendencies.

Graham Smith, the chief executive of Republic, says he expects more such evidence of interference to be revealed in the coming weeks. He joined the group in 2003 as an idealistic, left-leaning, Bristol-born former backpacker. As a 12-year-old he remembers asking to be excused from a classroom where Prince Andrew's wedding to Sarah Ferguson was being shown on television. Republic, which emerged in the early 1980s, had about 300 members and little direction when Smith, now 41, arrived after a period of living and working in Australia. By 2006, he had taken on the campaign and it now has more than 5,000 paying members as well as about 35,000 online supporters.

Resources are limited – the group has only two full-time members of staff and an income of £140,000 last year – but Smith views public apathy as progress, and an opportunity for growth. "Opinion has shifted away from the monarchy in the sense people don't care about it," he says the day before the Leeds event at Campaign HQ, his modest two-up, two-down in St Albans (he hopes to find some office space in London by the end of the year). "And they haven't shifted towards us because they haven't had the opportunity to think about it. But when you start talking to them about the issues, they quickly change their minds."

This becomes evident in Leeds after Mrs Adkin leaves to continue her shopping. In an hour of leafleting, Republic encounters only one other monarchist. When a campaigner hands Michael McGann a leaflet and the man glances at it, he turns to his young son. "Now that is what you call a tosser," he tells the boy. As he leaves the square, he explains that he was raised a royalist. "My mum and dad got a telegram from the Queen when they were married 60 years," he adds.

Members of the Republic organisation - Grant Buckley, Nigel Catling and Mark Sutton - meet in a Leeds pub earlier this month (Victor De Jesus/UNP)

Mr McGann and Mrs Adkin won't be swayed but everyone else on the square is sympathetic, to varying degrees. "I mean, we're living in 2016 so I don't really see why the Royal Family should have these privileges," says Sam Ero, a Nigerian who has lived in Leeds for eight years. Carla Martinez is about to start a shift at a nearby clothes store. "I do think it's a lot of money that goes to waste," she says, clutching the third leaflet available today. It presents Republic's estimation that all royal expenses, including unlisted security costs, amount to £334m a year, almost 10 times the official figure.> It also challenges the widespread view that the Royal Family is good for tourism, evidence for which, it says, is scant.

The Charles revelations last year coincided with a potentially favourable political wind for British republicanism. Jeremy Corbyn's election as Labour leader last September triggered fierce constitutional debate after the veteran republican hesitated before agreeing to kiss hands with the Queen when he was sworn into the Privy Council. But since then, and the grief he also received for not singing the national anthem at a Battle of Britain ceremony in September, he has parked his republicanism as a low priority.

In Smith's front room at his home in St Albans, a draft of Republic's "Royal Secrets" report sits next to a BBC Daily Politics mug. Smith says Corbyn has been a trigger for debate, as well as media appearances for Republic. But he also admits to concerns. "I think most people have no particular idea of what a republican is, but if there's a stereotype it's probably Corbyn," he explains. "People think we are instinctively unpatriotic and left-wing … And there is a danger that if Corbyn is unsuccessful, there could be some sort of blowback for us in the sense that it might reinforce the stereotype."

Either way, politics is bringing new attention – and members – to Republic. Daniel Cale, 22, has joined the group in Leeds after receiving a Republic leaflet at the anti-austerity marches in London last summer. "I never agreed with the institution but I never knew there was a campaign group," he says. The only woman among eight people who eventually show up today has heard about the group on Twitter, she thinks in a tweet by a Corbyn supporter. Both newcomers live in Leeds. "I wanted to get a feel of your aims and objectives," the 40-something (she asks not to be named) tells the men. "I don't understand how you can have hereditary advantage in a democracy."

Republic presents itself as a politically neutral pressure group. The Leeds network boasts about a Conservative councillor among its ranks. It has also set its sights on a more significant, if even less obvious ally. "We're only a few years from King Charles and he's our greatest recruiting sergeant," says Professor Stephen Haseler, director of the Global Policy Institute and an expert on constitutional monarchy. Haseler, 72, is a former chair of Republic and is old enough to remember the age of deference. "Even 20 years ago it was almost taboo to talk about this," he says by phone. "Now it's acceptable but nobody is prepared to go beyond that and that's because of the Queen. The minute she goes, that's when monarchy becomes the big issue."

He describes the Queen as a "sticking plaster" whose 63-year reign has bridged incomparable eras. "Charles will be king right away – there's no gap," he says. "It will be the first succession most people will remember and the first of the modern democratic era. We will watch the hereditary principle in action and I think a lot of people are going to say, 'hang on a minute, where do we come into this?'"

Republic plans to channel its energies not into the all-consuming period of official mourning that will follow the Queen's death, but Charles's coronation several months later. "We're still fleshing it out but we're going to be quite vocal in saying that we can't have this guy walk into the top job just because his mum was doing it before," Smith says. "We will have a controversial figure as monarch, who people are already happy to criticise and attack, and that's a significant change from where we are now."

Graham Smith of Republic in his office in St Albans (Victor De Jesus/UNP)

By the time of accession, Smith also hopes Republic will also have grown. He wants to attract at least 2,000 new members this year. While he challenges some parts of the media, including the BBC, over its "soft" treatment of the monarchy, he also knows that saturation coverage of big events is good for Republic. It gained 500 members during the 2011 Royal Wedding. The group is also growing its social and old media presence, and has a loose network of 10 volunteers who lead its investigations, in particular its Freedom of Information work. And at a local level, 21 groups are now bringing Republic's case to the streets.

At midday, the Leeds contingent leaves the square and heads to a pub for a meeting, details of which were posted on the national group's website. An hour or more of discussion follows, much of it repetitive. The average age is above 50 and there is a heavy leftward lean (the Tory councillor couldn't make it). Eventually, Mark Sutton, who co-ordinates the group, talks through some of its plans for the year. They include a stall at the Green Party's spring conference in Harrogate in February, and Ukip's main conference in Doncaster in the autumn. Sutton, who is 50, was at Ukip's gathering last year. "Surprisingly quite a few of them were on our side," he says.

It would easy to think that, despite Republic's growth and growing confidence, as well as the perceived threat to the stability of the monarchy posed by a king called Charles, the monarchy remains as rooted in the British landscape as the Jubilee tree in Leeds. Perhaps its greatest protection is the prime minister of the day, whose own role would be reduced without the patronage of the honours system and the powers that come with the royal prerogative. The current Prime Minister also happens to be a big fan – a 14-year-old David Cameron camped out overnight to watch the wedding of Charles and Diana in 1981.

But Smith believes that change will arrive in his lifetime, and will come from the bottom up, regardless of who occupies Downing Street. "Look at the Scottish independence campaign," he says. "Right up until six months before the referendum, support was somewhere around 30 per cent. A lot of that was because many people hadn't made the leap of imagination required to think about what an independent Scotland would look like. Or think about the massive turnaround in public attitudes about gay marriage, or environmental issues," he adds. "You can change minds quite quickly."