Campaigners have criticised local authorities that “subsidise” the work of trade unions by giving them free office space.

The Taxpayers’ Alliance says 273,753 square feet of dedicated office space was given to trade unions in 2013/14 – more than the total floor space of the Grand Kremlin Palace in Moscow.

The amount of office space would have a market value of more than £25 million in London – but an investigation by the campaign group revealed only £307,000 in charges was recouped by public sector organisations.

Trade unions at East Sussex County Council take up 1,400 square feet of office space, worth in the region of £25,000 a year.

Union staff at Brighton and Hove City Council use 710 square foot valued at about £17,000 a year, while West Sussex County Council union staff used 613 square foot worth in the region of £5,000.

None of the three councils charge the unions for office space use. Worthing, Adur, Arun, Crawley and Horsham did not respond to the Freedom of Information request.

Jonathan Isaby, chief executive of the TaxPayers’ Alliance, said: “It’s completely inappropriate for public sector bodies to be subsidising the work of trade unions which take great pride in disrupting essential services, especially after government guidance has told them not to.

“The drastic difference between the value of this space and the pittance that unions have to pay for it is striking.”