Monday January 22 is a red letter day for the union as its address will change from 75-79 York Road, London SE1 7AQ to New Prospect House, 8 Leake Street, London SE1 7NN. Telephone numbers and email addresses will be unchanged.

Prospect General Secretary Paul Noon said: "We are delighted that the architects Austin-Smith:Lord and engineers Rybka have produced a cutting edge design that combines modern, high quality office and meeting space, with best practice in environmental sustainability.

"The high performance envelope will make the building extremely energy efficient enabling us to minimise the amount of energy needed to heat the building during the winter or keep it cool during hotter months. There are a number of other environmental features of the building including solar panels and a 'green roof'.

"The move marks a new era for the union and provides an ideal modern base from which our negotiators can represent members in discussions with employers, Parliament, the TUC and other organisations."

The union’s 80-plus London staff will occupy the basement and first three floors of the five-storey building. The two top floors have been let to another union, the First Division Association, who will move in soon after Prospect.

Prospect represents members working across a broad range of professions covering archaeology, defence, science and medical research, energy and electricity supply, agriculture, administration, industry, environment, transport, heritage, law and order and health and safety.

In addition to the London headquarters, Prospect offers support to its 102,000 members via seven regional offices based in Bristol, Cardiff, Chertsey, Edinburgh, Liverpool, Lutterworth and Rotherham.