More than 1,000 companies are now committed to paying the living wage or above, securing tens of millions of pounds in extra pay for the working poor, it will be announced on Monday.

The surge in numbers, and the burgeoning campaign to lift the pay of the worst-off, means that about 60,000 people will be given a pay rise after Monday when a new higher living wage rate is announced. The current rate is £8.80 in London and £7.65 elsewhere.

In 2013, 432 companies were accredited by the Living Wage Foundation, a part of the community organisation Citizens UK. That figure has now more than doubled, as hundreds of other organisations, charities and businesses have signed up.

The Department of Energy and Climate Change pledged on Friday that all its subcontractors would pay the living wage, becoming the first Whitehall department to be formally accredited by the foundation.

It joins a host of leading companies, including Google, Barclays, Goldman Sachs, ITV and Legal & General, in making the commitment to be a living wage employer, remunerating all employees well beyond the legally enforced £6.50 national minimum wage.

An independent evaluation of the living wage initiative funded by Trust for London, to be published on Monday, calculates that by September 2013 the living wage campaign had generated £48m in additional wages for 23,000 low-paid workers. The huge increase in accredited companies since then means those “gains have significantly increased”.

Neil Jameson, executive director of Citizens UK and one of the founders of the living wage campaign, which was launched in 2001, said: “We have a great deal to celebrate but there is still much to do. Our aim is to influence the coming general election and have 5,000 accredited living wage employers by 2020.”

Other government departments paying the living wage include Iain Duncan Smith’s Department for Work and Pensions and Sajid Javid’s Department for Culture, Media and Sport. However, those departments have yet to sign up with the foundation to signal their sustained commitment, while other government departments have a poorer record.

The Department for Environment, Food and Rural Affairs, headed by environment secretary Liz Truss, and HM Revenue and Customs (HMRC), whose chief executive is Lin Homer, continue to refuse to ensure that all their subcontracted staff are paid the living wage.

A spokesperson for HMRC said: “HMRC greatly appreciates the work cleaning staff do in our buildings and all cleaning staff are paid above the national minimum wage. As cleaning staff are employed by an external contractor who sets the terms and conditions of their employment, HMRC has no control over their pay.”

Labour has pledged to give tax rebates to companies that sign up as living wage employers in its first year in power if it wins next year’s election. It will also require listed companies to report on whether they pay the living wage and is looking at how all government departments could encourage subcontractors to step into line.

The Green party has called for the national minimum wage to be lifted to £10 an hour immediately and then continue to reflect the cost of living.

The living wage is voluntary and set independently by the Greater London Authority in London. Loughborough University sets the rate outside the capital. It is calculated according to the basic cost of living in the UK and to allow an employee to earn sufficient to also have family time.

The mayor of London, Boris Johnson, a supporter of the living wage, as was his Labour predecessor Ken Livingstone, will visit Kaffeine, London’s first living wage coffee shop, on Monday to announce a new improved London living wage rate before visiting the London headquarters of Google.

Other companies to sign up this year include Ogilvy & Mather, the global communications company, the food company Nestlé and Heart of Midlothian football club.

Hearts owner Ann Budge said she was proud that it had become the first club in Scotland to pay the living wage. She said: “We believe it is entirely in keeping with the values we hold dear as a club.”

The living wage differs from the national minimum wage – set at £6.50 per hour for those aged over 21, £5.13 per hour for those aged 18-20, £3.79 per hour for under-18s and £2.73 per hour for apprentices – which is set and imposed by the UK government and bound by law.