They take up position outside train and underground stations in all weather, smartly dressed, courteous and smiling. They are sometimes called God-botherers or Bible-bashers – but this army of polite, freshly-laundered missionaries neither bother nor bash. They may stretch out a hand to offer a pamphlet to commuters streaming past, but they rarely accost anyone.

In fact, on the rare occasions when a passer-by does show interest, the proselytisers seem faintly surprised. “Could I have one of your pamphlets,” I ask a young woman outside a London railway station. “Of course,” she replies – but I have to make a further request for a second title, and at no point does she try to engage me in conversation.

Jehovah’s Witnesses – for indeed, it is they – are stepping up their presence in city centres across the UK in an effort to attract converts to a church that claims more than 8 million adherents worldwide. Best known for door-to-door evangelism and persistent attempts to engage householders in conversation about God, Witnesses are increasingly to be found in shopping centres, stations, parks and squares in at least 13 cities in England, Scotland, Wales and Ireland. In London, more than 1,000 people regularly participate in “public witnessing”, handing out 6,000 brochures, 20,000 books and 100,000 magazines each month. In other cities, the number of volunteers averages around 200.

According to Jehovah’s Witness full-timers, the results have proved the value of the new approach, although figures prove elusive. “It’s hard to quantify by number ... but a lot of people express appreciation of the work we’re doing,” says Mark O’Malley, who is “assigned” to the public information desk at the Jehovah’s Witness UK centre in north London. “We now have more than 165,000 [literature] carts on the streets in over 50 countries. It gives us visibility and availability. It’s something we’re going to see more of, definitely.”

All those baptised as Jehovah’s Witnesses are required to proselytise, logging the number of hours spent in doorstep and city centre evangelism in a monthly “field service report”. A standard commitment to ministry work is 840 hours a year – more than 16 hours a week. “This is not the kind of movement where you can tag along for a free ride,” says Andrew Holden, author of Jehovah’s Witnesses: Portrait of a Contemporary Religious Movement.

“Jehovah’s Witnesses have always been an aggressively evangelistic organisation since inception. Proselytising is central to the modus operandi. They see it as a fulfilment of biblical prophecy,” he says. The move to public witnessing follows an increasing awareness of “how busy people’s lives have become, that people are often not at home. So door-to-door evangelism doesn’t really win many converts. And for every recruit, there are hundreds and hundreds of rebuffs.”

Before they are let loose on the public, JWs must first fill out an application form, asking such questions as “Are you now of good moral standing and habits?” and “Are you willing and able to follow theocratic direction on public witnessing?” A section of the form asks the local “congregation service committee” to rate the applicant on a scale from A to E on four criteria: dignified personal appearance; dependable and organised; balance in judgment and discernment; and physical stamina.

Spreading the word … a Jehovah’s Witness at a central London stall. Photograph: Sean Smith for the Guardian

An internal letter sent to “all bodies of elders” in November 2012 issued detailed guidance on public witnessing, saying “it has proved to be an increasingly effective means to reach many with the good news of the Kingdom”. Amid advice on locations and display techniques, it adds that public witnesses “should present themselves in a dignified way. Their appearance and dress should be professional, well-arranged and modest.”

According to Holden, JWs are given careful instruction in proselytising, including role-play and detailed assessment of criteria such as eye contact and fluency. Individuals are given a personal assessment report to study in order to improve their performance. “The training involved in effective communication for the sole purpose of winning recruits is not unlike that undertaken by sales personnel in the secular world of business,” he wrote in an academic paper in 2003.

Simon Darling, who grew up in a Jehovah’s Witness family and was baptised into the church at the age of 15, spends his weekends in public ministry at an assigned spot among around 20 locations in central London. He is unsurprisingly enthusiastic about the practice. “It’s excellent. If I’m honest, what I’ve found is that people who I would never have approached have come up to me. We all make snap judgments in our heads about whether someone might be interested, but this allows people to come to us.”

This doesn’t quite square with an hour I spent watching six JW stands at Oxford Circus underground station one busy lunchtime this month. The only person I saw approach asked not for a copy of Awake! or The Watchtower or What Does The Bible Really Teach?, but for directions.

'Knocking on doors has long been immensely unpopular. It’s embarrassing. Often you’d just pretend to ring the doorbell'

Former JW Robert Crompton says: “I’ve certainly noticed the carts everywhere. But quite frankly, a lot of us ex-JWs find the whole thing quite amusing. Knocking on doors has long been immensely unpopular [among JWs]. No one likes doing it. It’s embarrassing, you get rebuffed, often you’d just pretend to ring the doorbell. But with these carts, you can just stand there, not doing anything and not talking to anyone, just logging your hours.”

The 2012 letter emanated from the Christian Congregation of Jehovah’s Witnesses, headquartered in Mill Hill, north London. It is a huge place, known in JW parlance as a “bethel” (house of God), where 800 JWs live and work. But, apparently, not huge enough. Work will start next year on a vast new £150m complex near Chelmsford, Essex, constructed entirely by volunteer labour. A model shows residences for 1,200 people, offices, printing plant, auditorium, hospital, fitness centre, water treatment plant and parking for more than 1,000 vehicles. I ask O’Malley, a former Catholic whose entire family became Witnesses when he was 10, if there were any objections at the planning stage; after all, not everyone wants Jehovah’s Witness Central in their back yard. “I think the council was happy that we were buying, clearing and developing the site,” he says.

At Mill Hill, the centre and residences are spread over several smaller sites. The day starts with the study of the scripture set for the global JW membership, followed by the standard working day from 8am until 5pm. “Bethelites” are assigned jobs and given training where necessary, for which they receive a stipend of £100 a month, with all necessities provided.

O’Malley hosts me for lunch in the dining room, where we are joined by fellow bethelites Andrew and Jane Schofield. On a hot June day, the men are wearing immaculate suits and ties; Jane, who is assigned to housekeeping duties, wears a cream skirt, floral blouse and suede ankle boots. Witnesses are instructed to dress modestly and presentably at all times. When I ask Schofield how bethelites afford such nice clothes on their modest stipend, he talks vaguely about donated items. On the day of my visit, lunch was roast lamb, roast potatoes, cabbage and carrots, followed by dessert and coffee. What happens if you’re a vegetarian? “There are vegetables,” shrugs O’Malley, as if no one has ever demanded a choice. Dinner is served from 5pm until 5.45pm.

JWs place great emphasis on personal as well as spiritual hygiene, cleanliness being next to godliness. The Schofields and O’Malley each separately tell me about the laundry facilities at JW headquarters. While showing me the printing plant in which millions of booklets are produced each year, O’Malley points with pride to the glossy polished concrete floor and gleaming machines. It is unlike any other printing plant I have seen.

Strict rules govern the lifestyle of Witnesses. “We stick by the Bible’s moral codes,” says Schofield. These include, he says, no sex outside marriage, no homosexuality, no smoking, no drugs (“though of course the Bible doesn’t talk about drugs,” he concedes) and only moderate alcohol consumption is permitted. Films, television and the internet are not banned, but Witnesses are “discouraged from viewing immoral or excessively violent” content. “We put an emphasis on a ‘Bible-trained conscience’ – a framework for life.”

The internet – “a wonderful tool, but with a sinister side,” according to Schofield – has been harnessed by Jehovah’s Witnesses, with a website (jw.org) in 540 languages, a broadcast channel (tv.jw.org) and various apps. In the first two years following the launch in August 2012, 850m visits were made to the website, according to the most recent JW yearbook. “We’re very ahead with technology,” says O’Malley, pulling up today’s set scripture on his smartphone. Later, he says: “We’re like Google – we’ve mapped the world.”

The global church is run by a seven-strong, all-male, self-selecting Governing Body, based in Brooklyn, to which all Witnesses defer. In the UK, a registered charity, the International Bible Students Association, runs the printing operation that churns out publications in 700 languages. The Watchtower Bible and Tract Society is the New York-based Jehovah’s Witness company responsible for the church’s administration. In 2001, Newsday listed the Watchtower Society as one of New York’s 40 richest corporations, with revenues of more than $950m. The organisation says it is financed entirely by voluntary donations, with no system of tithing.

Essentially it is Bible quotations with dire warnings, firm advice and tales of personal redemption ... The Watchtower Photograph: Guardian

Awake! and The Watchtower, the JW’s regular giveaway magazines, are essentially quotations from the Bible strung together by dire warnings, firm advice and tales of personal redemption. For example, the May issue of Awake! (print run: 51.7m) includes a section on “Teaching Children to Obey”, exhorting parents to “assert your authority”, quoting Proverbs 23:13: “Do not hold back discipline”.

The Bible is viewed by JWs as a historically accurate document and the absolute authority by which adherents live. Since the organisation was founded in the 1870s, its followers have believed humanity is living in the final days before the second coming of Christ, and has repeatedly prophecised Armageddon. “Islamic terrorism, tsunamis, earthquakes – they’re all seen as a fulfilment of biblical prophecy,” says Holden. But, he adds, given that the end has not materialised on the anticipated dates, “it is all the more surprising that the society has continued to recruit and expand with the success it has”.

These millenarians reject the doctrine of the holy trinity, refuse to celebrate Christmas or Easter (or birthdays), and avoid contact with “worldly” people (non-JWs) who are seen as morally corrupt. All other religions are considered false, ruling out ecumenicalism. Members are not allowed to challenge or debate the pronouncements of the Bible – or the governing body.

Most famously, JWs refuse blood transfusions, even when life is at risk. They say the Bible instructs the faithful to “abstain from blood”, which rules out accepting transfusions. “It’s a direct command in the Bible, but we also increasingly see medical evidence showing the advantages of not accepting blood transfusions,” says O’Malley. He cites the 2010 Haiti earthquake, when the National Blood Transfusion Centre in Port au Prince was destroyed, causing a critical shortage of blood and equipment, and says many people survived “bloodless” surgery. In fact, the World Health Organisation, Red Cross and medical charities made desperate appeals for international blood donations in order to save lives.

Many believe the Jehovah’s Witness organisation to be a global cult, escape from which is difficult and distressing. Bonnie Zieman, whose book Exiting the JW Cult: A Healing Handbook was published in May, speaks of her years of “submission” to the “toxic ideology” of a controlling and repressive sect.

She recounts how when she and her husband left the JW, their families “slowly began to cut us off. We are now not invited to family events such as weddings, funerals, family reunions; nor are we informed of births, accomplishments, illnesses or deaths in the family.” She adds: “Exiting the JW cult was one of the hardest things I have ever done, and one of the very best. I have never regretted it.”

Others’ experiences echo Zieman’s. Crompton, who was formally “disfellowshipped”, or expelled, 40 years ago, was “shunned” by his family. Having grown up in a JW family, “it took a long time to develop the normal social skills that most people get simply by growing up. I was entirely alone for a long time.”

Lloyd Evans formally left the JWs in 2013, three years after “I woke up from indoctrination”. He says: “It’s impossible to leave without punishment inflicted on you. I’m paying the price of something that happened when I was 11 [his baptism].” He is now “shunned” by his father and sisters. “My baby daughter has never seen her grandfather.”

Evans claims JWs are increasingly trying to win over children as adults become more sceptical about the nature of the organisation. “They are getting hammered on the internet. You can push any amount of [JW] material into people’s hands, but then they go home and open Google, and the whole thing collapses. The more you look at Jehovah’s Witnesses, you realise they are a fantastically successful cult.”

Other former JWs have alleged sexual, emotional and psychological abuse, domestic violence, the loss of autonomy, the denial of education and people driven to suicide or to attempt suicide. In June, a British woman won a £275,000 payout after a court ruled that JW elders had failed to protect her from sexual abuse as a child, in the first case of its kind brought in the UK. The judgment came two months after a California jury awarded a woman $28m in damages for child sex abuse. The Witnesses’ legal entity was ordered to pay almost $24m of the total after it was held responsible for covering up the abuse.

Holden points out that mainstream religions, including the Catholic church and the Methodists, have also seen cases of child and sex abuse. “I prefer the term religious movement to cult. JWs may not appeal to many people, but we need to be careful about branding them a cult. They’re not particularly renowned for doing dangerous things.”

O’Malley dismisses claims of a cult. “Anyone can make accusations, but that doesn’t make it the truth. People say things all the time. We’re not on a campaign to try to counter that, we’re just going to continue. We’re not embarrassed about anything we do.”

Back at Oxford Circus, there are plenty of takers for free samples of Lipton Ice Tea and the London Evening Standard, but none for Awake! and The Watchtower. Undeterred, Luis and Veronica, a married JW couple from northern Spain, politely tell me they are happy to spread the truth during their four-hour stints. “It’s wonderful,” says Luis, sporting the ubiquitous JW smile.

Are they taught to smile, I ask Andrew Schofield at JW HQ. “God loves a joyful giver,” he replies – with a smile.