Image copyright Merline Chambers Image caption Merline Chambers is among those campaigning for the London Living Wage

"It's a struggle to make ends meet from month to month," says Merline Chambers.

She works at the government's Department for Business, Energy and Industrial Strategy (BEIS) and is campaigning to be paid the London living wage.

A worker in the coffee shops inside the government department, she is one of the 100 or so members of the Public and Commercial Services union (PCS) who are striking to be paid at least the London living wage of £10.55 an hour.

The workers assembled outside the BEIS building in central London tell the BBC they are paid at rates between just above £8.21 per hour - the statutory National Living Wage - and other levels under £10.

Their small but loud protest - the catering and security staff are blowing on ear-splitting yellow horns and blasting out music - is taking place in the shadow of the Palace of Westminster.

BEIS says it recognises that staff deserve "a fair wage for their hard work".

'Using credit cards to survive'

Catering staff - largely contracted from Aramark - are striking for five days and porters and security staff - largely employed via ISS - for three days.

Ms Chambers, employed by catering company Aramark which took on the contract a year ago, has worked in the coffee shops for more than 10 years.

"Rent goes up, every January my fare to work goes up, gas and electricity goes up all the time. My shopping bill is always going up," she says.

Colleague Clive Willoughby interrupts to explain how he receives about £800 a month, spends £550 on rent and £85 on a bus pass.

"Some people are using credit cards to survive," he says. "They need to look at [the high] interest rates".

Others campaigning for higher wages are security staff working for outsourcing company ISS, which took on the contract in March.

Carl Torsu and his co-worker Adane Asfir are supervisors working opposite shifts in the control room in Beis.

Image copyright Carl Torsu Image caption Carl Torsu (right) and co-worker Adane Asfir have worked in the department for more than 20 years

"We are in the control room. We man the cameras, we see to the function of the guards [on the door] and tell them what to do," says Mr Torsu.

They explain that they have been required to train new controllers who were brought in on wage rates twice as high as theirs and in positions which were not advertised.

"We expect to climb the ladder and be managers by now," says Mr Torsu.

They list the numerous companies they have been transferred between during their 22 years at the department - illustrating the life of workers in outsourced industries.

Money is tight. "I'm always robbing Peter to pay Paul," says Mr Torsu.

They have received pay rises but not to the extent they argue they deserve.

PCS, which represents the workers, argues that the contractors should pay the London living wage and that business secretary Greg Clark should put pressure on ISS and Aramark to pay workers properly.

A Beis spokesperson said: "We have ensured that our contractors align the pay of cleaning, catering, mail room and security staff to the median rates for comparable occupations as identified in the annual survey of hours and earnings."

Image copyright @BEIS_PCS_LS Image caption On Monday, strikers offered Jamaican chicken to passers-by

On Friday, some of the workers on strike intend to head to Tunbridge Wells - Mr Clark's constituency.

Mark Serwotka, general secretary of the PCS said: "To take one day's strike action takes guts. But to run a sustained period of industrial action is heroic.

"Greg Clark needs to heed the message staff in his building are sending him."

He has previously said that ISS has not been paying staff on time and led to some to rely on a food bank set up by the local union branch.

'Long-running dispute'

The workers have already been on strike earlier this year.

A spokesperson for ISS said the company was disappointed with the decision to take industrial action and was committed to working the employees and the department to "encourage resolution".

"This is a long-running dispute that predates ISS taking over the contract at BEIS, with employee terms and conditions remaining unchanged from those offered by the previous contractor.

"We offer pay levels at the median rate for each profession, as identified in the annual survey of hours and earnings," ISS said.

Rebecca Long Bailey, shadow business secretary, said: "It is beyond disappointing that the department responsible for workers' rights has failed to treat and pay its workers properly.

Before the government departments were reorganised in 2016, the PCS said the former Department of Energy and Climate Change had agreed to pay the living wage.

PCS said that is still the case for workers in the Department for International Trade, now in the DECC building.

Aramark has been approached for comment.