As the marriage of Prince William and Kate Middleton approaches, some republicans believe the death of Elizabeth may bring the reign of the Windsors to an end - but is that what the public really wants?

Hugh Ashton's face was a portrait of thwarted ambition as he watched from a discreet distance the anti-monarchist protest in front of Buckingham Palace. He had come from Chichester, West Sussex, to take part in the illegal gathering, but couldn't bring himself to join the chanting republicans gathered at the gates of the enemy.

"It's a bit disappointing. I was expecting more people than this. It's made me wonder, if this is the strongest number they can get out... I was sort of hoping the police might move them on, but there's no edge to this at all is there?" Indeed, there was not. Two police officers watched impassively. They had another four community police officers to call on if things got out of hand.

Demonstrations are not permitted in the pedestrianised area between the Victoria Memorial and the palace's east front, from where Prince William and his bride, Kate Middleton, will perform the nuptial kiss on the balcony overlooking the crowds of well-wishers on 29 April.

A French tourist was explaining to fellow sightseers that the inscrutable cops had probably been advised not to take any action in case it encouraged other protesters. "It's not exactly Libya, is it?" he sneered. The Japanese visitors took turns to duck in front of the protesters and have their photos taken, fingers raised in the V for victory sign. Inevitably the media outnumbered the 25 protesters. Perhaps there were more wannabe republican demonstrators hanging about the edges like Ashton. "I think five minutes would have been enough," he muttered as the protest lingered on past the half-hour mark, breaking into another chorus of protest songs around the theme of royal secrecy (the government has exempted the monarchy from freedom of information legislation). "These are all heartfelt sentiments, but I'm going to go to the pub now. I am a lone voice in Chichester."

Graham Smith doesn't share the pessimism. As the only person in the UK who draws a salary for promoting republicanism, he takes a professional approach. The campaign manager of the organisation Republic believes that royal weddings are good for business – if not quite as good as the Prince of Wales, whom he would like to make an honorary member. He points to last year's Swedish royal wedding, on the eve of which a poll showed that support for the country's monarchy was at its lowest: only 46%.

"It's a good omen for those of us who want a serious debate about the monarchy and our constitution," he tells a German TV crew. "The monarchy is not a luxury; it's an imposition and an obstacle to serious political reform." British public opinion about the royal family is fickle, he says. "We are launching Republic 2025. We need to put a date on it because things that people don't expect can happen very quickly – just look at the Arab world."

But Britain a republic by 2025? The calculation is based on the longevity of the Queen, who Smith grudgingly concedes is unassailable "because she's been there so long, we've all grown up with her". When Elizabeth II departs it is game over for the Windsors, according to Republic. Even Tories, such as journalist Max Hastings, seem to agree about Prince Charles's potential for damage. "He is not a bad man, but I think he is a very dangerous one for the monarchy, if allowed to ascend the throne," the former Daily Telegraph editor wrote recently.

In an essay for the Institute of Public Policy Research, Labour MP and historian Tristram Hunt urged Prince William to steer clear of his father's "reactionary, anti-Enlightenment sensibility" and leave "the bling and conspicuous consumption to the Russians and Saudis". Hunt says millions view the monarchy with affection because at its best it represents "continuity, tradition and dignity", though for many on the left it is "the antithesis of everything we believe in". He concludes that "for better or worse we do have a monarchy which has numerous advantages in modern, multicultural Britain. Yet if it is to sustain itself, 'the firm' needs to continue to evolve."

Whether or not you agree, it is a good illustration of why Smith describes the status quo as "the politicians' monarchy – it serves their interests and not ours. The monarchy corrupts the culture of politics because the politicians end up seeing themselves as part of a state apparatus rather than the people's servants."

Hunt's good friend Lord Mandelson was not just a republican himself 30 years go, he flaunted it. All the way to France, in fact. In protest at the "royalist orgy" that was the wedding of Prince Charles and Diana, he hopped on a cross-Channel ferry with Harriet Harman and other Labourites to escape for the day to republican France. Three of the day-trippers now have seats in the House of Lords.

This time last year Mandelson was lord president of the Privy Council, presenting business from its monthly meetings for the monarch's approval. Harman served during the same period as lord privy seal. Alastair Campbell recorded in his diaries Mandelson's desperate efforts to get a place at Diana's funeral in September 1997: "Peter called from the US to try to get to the funeral 'as a personal friend'. He also called Mark Bolland (deputy private secretary to Prince Charles) and tried via him, saying he was setting up a phone call between TB (Tony Blair) and Charles. He just could not resist it. There was something pathetic about it."

The current lord president of the council is Nick Clegg, who Smith believes is, or at least used to be, a republican. The point of the Buckingham Palace protest was to call on Clegg to use his protection of freedoms bill to open up the monarchy to greater public scrutiny. "We know that most of the Lib Dems, including the cabinet members, are supportive of us. A lot of them have admitted it privately to us, but they are terrified of going public, of the repercussions and the electoral impact. They should take heart from Norman Baker [Lib Dem transport minister] who is one of our members. He's MP for Lewes. East Sussex isn't regarded as a hotbed of republicanism, and yet the issue hasn't affected his vote. The media hasn't caught up with the fact that most people are indifferent to the royals."

But it's a giant leap from indifference to activism on an issue which fails to register in the national discourse. Where are the young Mandelsons and Harmans of today? Republic can rely on the support of only 14 Labour MPs, the Green MP and two Liberal Democrat MPs.

Last week there was a telling encounter in the House of Commons. The Speaker, John Bercow, chided Chris Bryant, a former Foreign Office minister, for saying: "Isn't it time we dispensed with the services of the Duke of York?"

Prince Andrew's friendship with US billionaire and convicted sex offender Jeffrey Epstein made headlines this weekend, as well as news that the fourth in line to the throne entertained a leading member of the deposed Tunisian regime at Buckingham Palace last year. WikiLeaks revealed that a US diplomat described him as "cocky and rude".

As if this weren't enough to suggest the prince is a liability for Britain in his role as special trade representative, Bryant told the Commons of Andrew's friendships with Saif Gaddafi and the convicted Libyan gun smuggler Tarek Kaituni. Bercow intervened, telling MPs: "References to members of the royal family should be sparing and respectful. We have to be very careful in our handling of these matters." He was later forced to accept that only the monarch – not members of the royal family – was referred to in the parliamentary handbook, Erskine May, when discussing matters of decorum.

If the monarchy has never looked more protected by the political establishment (David Cameron slept out overnight on the Mall in 1981 to ensure he got a good view of newlyweds Charles and Diana), Smith believes that 20 years ago he would have faced far greater hostility from the public for advocating a republic. "That's gone and it's down to the royal family's own scandals, which have stripped away the veneer of magic. Society has become a lot less deferential. The royals have become a part of the celebrity culture, and that's what sustains them."

That may be true, but neither is there the noisy antipathy towards the royals which surrounded the 1977 silver jubilee. "Fuck the Jubilee" was the rallying cry of the punk movement and God Save the Queen by the Sex Pistols its anthem. Johnny Rotten today sells butter on TV ads and confesses he is a fan of Princes William and Harry. According to Mori founder Sir Robert Worcester, support for a republic has remained constant at about 19% since 1969 – except in the two weeks after Diana died, when it rose to 25% and then fell to 12% after the Queen broke her Balmoral silence on the tragedy.

The Germans, the Spanish, the French and the Japanese have nailed the true point of interest in the royal wedding: it is a romantic fairytale made flesh and blood for a global audience. "Right now most Germans are really excited about the wedding, they see it as really romantic and they are thinking about Diana," Michael Gartner of SAT1 German TV said. "Kate is on the cover this week of Bunte, the biggest magazine, and the wedding will be shown live on three national channels." He had to think long and hard when I asked him for the name of the German president. "It's Wulff, but nobody cares."