Leading heritage sites across the country were closed or severely disrupted as staff walked out between 10-12pm. Members based in English Heritage’s northern regional offices, such as York, Manchester and Newcastle, joined the two-hour walkout in the morning.

The dispute continued in the afternoon when normal business was brought to a standstill as staff in southern regional offices, including Swindon, Bristol and English Heritage’s headquarters in Saville Row, also left their desks to form pickets outside between 2-4pm.

The action was taken jointly with 300 members of the Public and Commercial Services union, and members reported widespread public support with a number of visitors refusing to cross picket lines.

Prospect negotiator Dave Allen said: "Our members regret any inconvenience caused but felt that they have been forced into taking a stand. Today’s walkout demonstrates the strength of feeling among members, not only over a derisory pay offer, but also at the wider financial crisis facing the organisation, which has already resulted in a cull of skilled staff.

"It has sent a clear signal to management that staff will not accept the imposition of another below inflation pay offer or its increasingly cavalier attitude towards industrial relations."

The action will result in a knock-on delay to many planning applications and requests for listed building consent. Prospect members work as conservators, curators, building inspectors, architects, archaeologists and surveyors for English Heritage.