The members of the Unite union downed tools between 05:30 and 08:00 over a refusal by Sellafield Ltd and the group of subcontractor companies to facilitate a full-time union convenor on the site.

Picket lines were also set up outside the entrances to Sellafield following an ongoing work-to-rule and overtime ban which has been in place since Friday 31 July.

The construction workers, working for 15 subcontractors, are pressing for the creation of a full-time convenor on the site.

Unite said they want the convenor “to improve industrial relations and help address growing health and safety concerns as well as poor welfare facilities on the construction site.”

Unite regional secretary Mick Whitley said: “Sellafield is an important nuclear facility where health and safety and the welfare of workers should be paramount.

“Our experience shows that a full-time union convenor would help ensure a healthier, more productive and profitable workplace.

“Workers want to work in a safe environment with constructive industrial relations. The continued refusal by Sellafield Ltd and the subcontractors to implement arrangements which are commonplace across the industry puts this reasonable expectation at risk.

“Our members are sick and tired of being treated like second class citizens on one of Europe’s biggest construction projects.

“We would urge Sellafield Ltd and the subcontractors to start treating their workers as partners and enter meaningful talks.”