The Enquirer understands around 50 sparks from the rank-and-file movement took part in the protest against the alleged removal of union members from the site.

The sparks claim union safety reps and electrical contractor EIS were removed from the Bam/Ferrovial/Kier consortium job for raising safety concerns – a claim fiercely denied by Crossrail.

Officials from the Unite union are believed to be in negotiations with the contractors and Crossrail.

A Crossrail spokesman said: “It is simply not true for Unite to claim that EIS workers had been laid off by Crossrail for raising safety concerns.

“All construction workers on the Crossrail project are employed directly by our principal contractors and their supply chain rather than by Crossrail Limited.

“A contract between our western tunnels contractor BFK and EIS ended early last week as the work they were carrying out to commission the first two tunnel boring machines had been completed with tunnelling now underway.

“Crossrail regards the safety of all those working on the Crossrail project as paramount and is committed to delivering Crossrail to the highest standards of safety at all times.

“Unite has never been prevented from discussing health and safety concerns or from approaching its members.

“In fact Crossrail encourages all those working on the project to take their safety responsibilities seriously and to raise any concerns through the reporting systems that are in place.”