Nearly 1,000 Prospect members at the government agency’s headquarters in Southampton, and offices in London and most other major UK cities, will work until noon before leaving their offices to stage protests outside. Shift and part-time workers will take action once they have completed half a normal day’s work.

Members voted overwhelmingly by four to one for strike action in a ballot completed last month but deferred announcing a date as talks continued to try and resolve the dispute. However, despite the talks OS has refused to offer any measures to address the demoralisation felt by staff over pay.

Prospect negotiator Ben Middleton said: "Members now feel they have no other avenue open to them other than strike action. OS management has failed to respond to their reasonable expectations to have pay protected against inflation and for staff to progress to the rate for the job in a realistic timeframe.

"We do not expect management to tackle all the pay problems for this and future deals at a stroke, and we recognise that all businesses face challenges in the future. But OS have stubbornly refused to acknowledge that staff who have patiently borne a succession of poor pay offers feel that patience has run out."

Ongoing action short of a strike will continue after Tuesday in the form of a work to rule and a ban on unpaid overtime on which OS relies to keep running smoothly.

Prospect represents specialist grades in OS in a range of roles including cartographers, surveyors, marketing and sales personnel, designers, and IT engineers. Members of Prospect’s sister union PCS will also be taking strike action.