The disruption was triggered when workers staged a sit-in protest on 2 June over safety concerns about new clocking-in stations, moved further into the job and away from canteens. Workers claimed the new clocking stations were dangerously close to a crane-lift zone which is denied by management.

Project bosses sent the M&E workers home after the action telling them to return a week later. Employers from the MEH alliance then took the position that those who had participated in the stand-down had taken unofficial industrial action and were acting unlawfully.

Workers were then told that those who had participated in the action would be required to attend individual HR meetings and could potentially face disciplinary action. This delayed the planned staged return to work.

The M&E workers were also informed that they would be required to agree to revised working arrangements, including a new 10-days-on, 4-days-off shift pattern that previously received a mixed response during workforce consultation.

The process has rumbled on with workers given the ultimatum to return to work on 23 June.

A source told the Enquirer: “It seems only 25% have returned, which is no surprise because the email ordered workers back late on Tuesday.

“Because many had returned home to areas like Scotland and the North East it was very late notice that arrived just before the England match.”

Another said: “Morale is at rock bottom at the moment, but most workers are expected to return to the job by Monday.”

The new shift patterns are due to come into effect from 7 July.