Every weekday Valdemar Ventura, a gentle man with impeccable manners, leaves his small flat in south London and, until July, made his way to Downing Street and the Cabinet Office, where his duties included cleaning the floors, lavatories and office of the deputy prime minister, Nick Clegg. "A good man," Ventura says. "He always said, 'Hello, good morning'."

Acknowledgment matters to a workforce often rendered largely invisible. Ventura, 44, a former soldier, came to the UK from Angola 10 years ago. Now he is one of 150 Whitehall cleaners, supported by the community organisation Citizens UK, campaigning for a living wage, the minimum hourly wage necessary for housing, food and other basic needs, calculated annually.

The minimum wage is £6.19 an hour. Ventura earns £6.95. A London living wage would see his rate rise by almost £2 an hour to £8.55 (£7.45 outside London). He works from 5am to 2pm before picking up his 11-year-old son, Enivalde, from school. (His other son, Enio, 22, is studying to be a pilot, to his father's immense pride.) Ventura's wife then works her shift. She also works part-time as a cleaner in the Cabinet Office while she studies for a qualification in human resources. She does not wish to be named for fear of the retribution that has now befallen her husband.

In July, Ventura became the "face" of a protest in the media. A group of cleaners wrote and delivered a personal letter to the ministers of eight departments, politely making the case for a living wage. Most cleaners were too frightened to be identified. The day after his photograph appeared in the press, his employer, ETDE, a subcontractor ("Our values are embodied by respect, a commitment to practise what we preach") suspended him for a day and moved his work from Downing Street to King's College in Waterloo.

At a disciplinary hearing in September, the company found him guilty of "gross misconduct", gave him a final written warning and charged him with "a security breach". It also chastised him for "unauthorised interviews" with the press. Paul Cadman of ETDE says Ventura was moved because "we could not be confident that he would not breach security again". (OCS, a subcontractor providing cleaners to the Treasury, acted far more leniently to another cleaner who spoke out in support of the voluntary living wage.)

The move was an affront to Ventura. Two weeks after he was disciplined, a King's College member of staff, unprompted, composed a letter to ETDE. "Mr Ventura does a fantastic job," she wrote. "The entrance and, dare I say it, even the architecture of the building is enhanced. He is a real asset to your company." Ventura shows me the letter and then says sadly: "My employers no longer see me as they did. But I am still the same. I am professional, my quality is still high. I just would like enough to give my family a life."

Ventura says his work has become more difficult. His contract states he is a "housekeeping operative". He must work from 5am to 9.30am with a tea break, "if time permits". He is allowed an unpaid hour for lunch before finishing at 2pm. His remit is singlehandedly to ensure that eight floors with several rooms on each floor are clean, including lifts, stairs and "internal glass polishing".

"I can't do it as well as I would like," he adds, plainly distressed. "It's too much for one person." He says he was also told not to talk to students. "This isn't a prison, it's a college," Ventura says.

The disciplinary move has hit Ventura's already threadbare pocket hard. Previously, he worked overtime on a Saturday, earning an extra £332 a month. That has been forfeited. Now he earns £14,500.97 a year with no overtime. Apart from child benefit, the family receive no other state support. Rent is £500 a month; bus fares £72 a month. Ventura has taken out a loan of £200, the interest payable over a year, with a money-lending company, Speedy Cash. The loan will cost Ventura £362.43.

A living wage would mean around an extra £200 a month; an end to ferociously high interest rates on instant loans, and a little leeway in the family budget so that his son, for instance, can join friends on outings and enjoy more of his favourite cereal. As a treat, his mother bought him Cheerios the other day. "I was very happy," Enivalde smiles.

Ventura is aware that his job may now again be in jeopardy, but he is determined to continue to campaign for the living wage. On Tuesday, he will explain his cause to 200 at a meeting of the west London branch of Citizens UK. "I can only use the power I have to fight, otherwise nothing will change," he says.

Stefan Baskerville, the Citizens UK community organiser responsible for Westminster, including Whitehall, says: "At the heart of what we are trying to do is to ask employers to take moral responsibility for the people who work for them, including the people who clean and cook and who carry stuff around the building, even if they are in subcontracted jobs," he explains. "Valdemar is a brave family man who has spoken up for the sake of himself and others. Someone at the Cabinet Office ought to take responsibility if he continues to be victimised."

And yesterday Clegg himself weighed in. "Valdemar always did a great job in our office," he said. "People should not be punished for campaigning for better pay. Creative and peaceful campaigns are part of Britain's proud history of freedom of speech."

The Whitehall cleaners' campaign began 18 months ago. It is not directed at the subcontractors. The goal is to persuade each government department to voluntarily pay the extra required to provide a living wage so subcontractors' profits are not affected. The intention is that only when the existing contract runs out would a living wage become part of contract compliance and future negotiations.

Five million people in Britain earn less than the living wage. Saturday saw the end of living wage week. It has been a good seven days for the campaign. Citizens UK announced that since the campaign's launch, in 2001, it has lifted 45,000 out of poverty. Last week 100 companies became officially accredited living wage employers, including KPMG, Save the Children and Linklaters, the legal firm; 10 Labour local authorities have committed to the living wage and nine more are on the way to doing so. Scotland announced it would incorporate the new rate in Scottish government pay policy, a move already made in Wales. The Living Wage Foundation was launched along with a new logo that hopes eventually to carry similar clout to the Fairtrade symbol.

In London, an estimated 11,500 workers have benefited since the London Living Wage was launched seven years ago, supported by Ken Livingstone, who was then mayor. His successor, Boris Johnson, has since also given his consistent support, going against his own party. In 2010, David Cameron promised that, since government is the biggest employer in the country, it would take the lead on "a good and attractive idea". He has now grown cooler on the living wage on the grounds that it could damage business. In contrast, last week Ed Miliband, the Labour leader, gave his full endorsement after a year of negotiations conducted by Citizens UK.

Last week Miliband, supplying more detail of what he meant by "responsible capitalism", said: "People often don't get paid enough to look after their families, to heat their homes, to feed their kids, care for elderly relatives and plan for the future. It's not how it should be in Britain. It's not how we will succeed as a country in the years ahead. Too many people are doing the right thing, but aren't sharing fairly in the rewards."

Miliband announced three policy proposals to promote the living wage: contract compliance in public sector contracts; paying firms a subsidy if they pay the living wage; and forcing companies to reveal how many of their employees are receiving less than the living wage. He told the Observer: "The living wage is about businesses, local authorities, civil society – the people of Britain – coming together with government to build a different kind of economy that works for all, not just the few at the top."

Back in Whitehall, there are signs of some support. Iain Duncan Smith at the Department for Work and Pensions has had a meeting; however, Vince Cable at the Department for Business, Innovation and Skills is definitely not keen. This is even though research from Staffordshire University Business School shows that payment of the living wage boosts local economic growth through increased consumer spending. Its study concluded that, for every extra £1 an hour paid to a low-paid worker, £1.63 is reinjected into the local economy.

According to Professor Jane Wills of the University of London, if all low-paid Londoners received the living wage, the government could save £823m a year by increasing the tax base and reducing welfare benefit.

Ventura's story is far from unique. Another cleaner talks of not being able to pay for plimsolls for his child's gym class; a third speaks of how the park is the main source of entertainment for his children because it is free.

Jasper Kain from Citizens UK intended to work on the Whitehall campaign for a matter of months. "Now, I'm here until we win," he says. "I'm completely attached to many of the people – they are people of such quality."

Many of the cleaners are from Spain, Portugal and Africa and would like to improve their English to acquire better jobs but their hours don't allow the time, he says, so they have skills but are stuck. They get by on little sleep, their health suffers, bad backs are part of the job. But, says Kain, they are a fraternity, looking out for each other, sharing money, for instance, when the wages don't stretch: "£2 an hour extra would make all the difference, not least because it would give them time with their families and a bit of dignity and respect."

Wesley's Cafe is in the basement of the Methodist Central Hall, Westminster. Every Friday lunchtime, organised by Citizens UK, Whitehall cleaners and mostly young civil servants come together informally to get to know each other. Relationships are the fuel of the living wage campaign.

On Friday, the chicken and mushroom pie, at £7.85, was more than a cleaner earns in an hour, so Citizens UK pays for food. Civil servants came from a variety of departments, including the Ministry of Justice, the Cabinet Office, and the Department of Energy and Climate Change, to chat and discuss the next stage of the campaign. One civil servant said: "This campaign isn't just about money and what's fair. It's also about a society in which we are all citizens. People show each other respect; we say, 'Hello, how are you?' to each other. We care. People aren't invisible."

Also present is Kofi Konan, a family man, originally from Ivory Coast. He had three jobs a day in Whitehall, cleaning and as a hospitality worker, until he became ill a few weeks ago. His working day began at 5am and ended at 10pm, to make ends meet.

A skilled musician, he is writing a song, an anthem to the living wage, with the help of Claudia, a Citizens UK volunteer and a French and history university student. It's a work in progress. "Pensez à nous," the song goes, "Spare us a thought, help make our work pay."