What do you need to earn per hour to support yourself in London? You won’t be surprised to hear that the national minimum wage of £5.52 per hour is nowhere near enough. In fact, research by the GLA’s Living Wage Unit shows that a wage of at least £7.20 per hour is what it takes to provide enough for the basics of life here in the capital.

Yet far too few of London’s workers receive this amount: around 400,000 Londoners fall into a ‘working poverty gap’, with their families receiving less than they need to get by. These families will be running up debts all year round, and as a result will be finding Christmas virtually impossible to manage.

So, that’s why I was more than happy to join the London Citizens’ living wage campaigners on Friday to sing myself hoarse as part of an audacious protest at the Tate Modern art gallery.

More about the protest itself in a second, but first I’ll explain why the living wage campaign is interested in the Tate gallery. South London Citizens (one of four major coalitions across London that make up the London Citizens organisation) has been trying to persuade the Tate to become a living wage employer for nearly a year, but still the board are refusing to ensure their 50 or so cleaners and catering staff are paid the London living wage of £7.20. Most of the cleaners are in fact on the national minimum wage and many have never received a pay rise above the minimum.

For a hugely successful gallery group, and one which is endowed with millions of pounds that came originally from the profits of a sugar industry that boomed thanks to slave labour, this is not good enough, so along we went on Friday to escalate the campaign.

A Christmas time protest at the Tate Modern is almost obliged to be both festive and arty, and the organisers had come up with something brilliant. It so happens that the gallery’s massive Turbine Hall is currently hosting artist Doris Salcedo’s installation of a 167 metre giant crack along the length of the hall’s floor, which appears to show the building literally coming apart. The piece is, among other things, a representation of the gap between the rich and the underclass in modern society, so it provided a perfect foil for our action.

Posing as a diverse range of ordinary art fans, around 100 of us waited for our signal (a lone singer and then lined up each side of the crack to link hands and solemnly sing together a range of Christmas Carols. After these songs, we filed out of the huge entrance doors – still singing – to join the more traditional union picket and brass band outside to continue performing seasonal songs with slightly doctored lyrics , including ‘we wish you a merry workforce’ (my favourite).

The effect of all this was so moving that we drew a large audience of spectators inside the gallery and the action inside was described on air as ‘incredibly impressive’ by the BBC reporter sent to cover it.

For me, the most impressive thing about the event was that a high proportion of the demonstrators were actual, in the flesh, vicars. This is because this highly radical campaign is being organised largely by faith groups and churches across London, alongside unions and student groups. Convinced by the rightness of their demands on behalf of the workers of London, these organisers are prepared to be more militant than most NGOs and are not afraid to be confrontational in their actions or scared to name and shame offending companies.

This radicalism means that they are really getting results, and hopes of eventual success with the Tate are therefore high. London Citizens’ work has already led to £10 million a year being paid in higher wages across London, with universities, hospitals and the Olympic Delivery Authority already committed to paying a living wage to their lowest paid employees. The Tate is clearly able to afford to pay all its staff decently, and the board cannot be happy at being shamed in such an eyecatching way at Christmas time by a group that includes so many Christians.

A similar protest at Citigroup in Canary Wharf at Halloween got a very quick response that means all their cleaners have the chance to support their families decently on their wages. In a city as rich as ours, there’s no reason why all big companies can’t do the same. I just hope we don’t have to send the vicars round to every one.