A prime, five-storey Victorian office building off Trafalgar Square in London has been taken over by a group of squatters who plan to open the building on Christmas Day and provide a free festive lunch for homeless people in a protest against the housing crisis.

Calling themselves the Love Activists, a group of 20 people on Saturday took over the grade II-listed building on the corner site of Charing Cross Road and St Martin’s Lane which has been empty for 18 months.

Previously leased by the RBS group and housing a branch of National Westminster Bank, the squatters say that the building has “been taken by the people” in a statement posted on their Facebook page. The current ownership of the corner site is unclear: Land Registry records show that the owner is Greencap Ltd, a Jersey company that appears to have been dissolved.

According to one of the activists, Danny Freeman, 22, the fact that the building was previously used by RBS, which was bailed out by the taxpayer during the financial crisis and today remains 79% owned by the state, has made their message of “homes not banks” all the more resonant.

Just days before Christmas, a group calling themselves the Love Activists occupy a former bank close to London’s Trafalgar Square. Video: Ross Domoney Guardian

Freeman said: “I have never before been involved in opening up a building of this size and scale. We hope to distribute clothing, set up a food bank and do some repair work so it will be in a better state when we leave than when we arrived here.

“We want to make this a safe space for all. We’re not equipped to deal with people who are violent or who have drug or alcohol problems.”

Built in 1890 by Robert Walker in Portland Stone and listed by English Heritage as a site of special historical and architectural interest, the property boasts a penthouse suite with aerial views of the capital, dozens of rooms, spaces for entertaining, and a secure vault in the basement.

The campaigners are hoping that the public will donate food and cooking utensils to help with their planned Christmas lunch for homeless people. Pete Phoenix, another of the activists, said: “We want solutions to the homeless problem so that people who have nowhere to live can use empty properties until the developers are ready to redevelop them. Homes for all for Christmas. Nobody should freeze.”

The squatters have draped banners outside the building with slogans including “seized by the people for the people” and say they have been speaking to passersby who have been largely supportive. Some of them have even given them money to help pay for the Christmas lunch.

The activists say they have a series of aims during their residency in the substantial building. As well as providing a safe, warm space for hungry, homeless people on Christmas Day, they are planning to run workshops and film evenings to highlight the widening gap between the rich and poor – with the bankers at the top of the financial food chain and homeless people at the bottom of it.

Also on the agenda are Spies Out of Our Lives, looking at the increasing incidence of surveillance and eavesdropping, and the We Can’t Breathe campaign, raising concerns about deaths at the hands of police and security staff.

A survey by the Empty Homes Agency has found that there are 610,000 empty homes in England, while the latest government figures reveal that on 30 September this year there were 60,940 households in temporary accommodation, as a result of homelessness, an increase of 6% on the same time last year.

Miguel, 31, one of the London squatters, said: “The reason why I’m here is for solidarity. This city belongs to the people, not the banks. If you go outside you can see lots of people sleeping outside in the cold and the wet.”

The activists say they have not received any formal communication from the owners seeking possession of the building. The closure of courts over the Christmas period is likely to delay any such action. One of the protesters, known as Mouse, said: “We have taken this building back for the people and hope we can hold onto it for as long as possible.”

A spokesman for RBS said that, since it handed the building back to the owners in June 2013, the bank no longer has an interest in the property. A spokesman for the managing agent, who asked not to be named, said that the owners were seeking legal advice.

But their true identity remains unclear. According to the Land Registry, a company called Greencap Ltd is registered at Ogier House, St Helier. But according to the Companies House website, Greencap Ltd has been dissolved.

A call to Ogier House in the Channel Island of Jersey revealed that Ogier House has now changed its name to Elian Private Wealth with offices in Bahrain, British Virgin Islands & Cayman Isles. Their website states that they are “specialists in corporate services, fund services, private wealth and capital services”.

A member of staff at Elian agreed to look into what had happened to Greencap but said later: “Unfortunately we are unable to assist with your queries.”

A spokeswoman for the London Borough of Westminster , where the building is situated, said that although the council has a policy to reduce empty properties as far as possible, if the company that owned this empty property was undergoing a change of management any action in this regard would take time.

She added that the council was not involved in any enforcement activity against the protesters. Assuming that the owners do seek a possession order against the squatters, they will have to reveal their identity at that point.

Meanwhile, the activists are making the most of the property while they can. While the government has made squatting in residential premises a criminal offence, squatting in commercial premises remains a civil offence.

Owners have to go to court to seek a possession order before squatters can be legally removed. One of the Love Activists told the Guardian: “We don’t usually find proper washing facilities in the commercial premises we occupy. The fact that there is a bathroom in the penthouse suite, so we can actually have a bath while we’re here, is a real bonus.”

He added that it was merely a happy coincidence that the National Portrait Gallery, which the current residents can see from out of their bedroom windows, is currently hosting an exhibition entitled Anarchy & Beauty: William Morris and his legacy 1860-1960. “We may well pop in and have a look,” he said.