On behalf of 170 members in professional grades at MCA, Prospect said the result reflected the anger among members at an offer which is below inflation, over nine months late and does not act on management’s commitments to remedy pay disparities.

On a 69% turnout, 87.1% of members voted in favour of industrial action short of a strike with only 15 members voting against.

It follows an earlier ballot held in February where members emphatically rejected a tabled pay deal that provided an average 2.5% increase for Prospect members – with less for the most experienced staff - at a time when the retail price index stands at 4.8%.

The action will take the form of a ban on overtime with staff only working conditioned hours and banning all out-of-hours coverage. Members will also stop using their own vehicles to travel to and from survey work that is required under UK law and international maritime safety regulations. The action is expected to lead to a backlog in the vital survey work undertaken at ports across the country.

Prospect negotiator John Ferrett said: "Our members’ expertise is vital to MCA’s work in preventing the loss of lives at sea and stopping coastal pollution. The below inflation award compounds existing frustration at the disparities in pay between MCA surveyors and comparable Department for Transport colleagues in the Marine Accident Investigation branch who are paid literally twice as much.

"Despite commitments secured by the union that management would prepare a robust business case for the Treasury to address this issue, the agency has refused to challenge the Treasury remit given to MCA. Our members’ patience with the repeated promises from the MCA board that there will be ‘jam tomorrow’ has finally worn out. You have to ask, given the threatened industrial action amongst other MCA staff, how long the agency thinks it can continue to disregard its’ staff?’

At this stage, said Ferrett, members have ruled out full strike action as they are crucially aware of the safety critical nature of their roles and their professional code. Members will meet next week to agree a start date for the industrial action.