Union officials are to take subcontractor Mechanical Installations International to an industrial tribunal after more than 70 workers were laid off from one of its schemes.

Officials from Unite said the company asked between 70 and 90 employees undertaking pipework on the £120m waste processing plant in Colnbrook, near Slough, to leave.

Developer Grundon said some had been replaced by “more specialised staff” from PJ Douglas Engineering and Fabricom.

A spokesperson for main contractor Takuma, said: “Employment levels at the plant fluctuate and will continue to do so depending on the requirements of the jobs in hand.”