Organisers of the demonstrations claimed that “300 electricians invaded the Crossrail Farringdon station construction project” this morning.

But a Crossrail spokesman said its Farringdon site was still at the groundworks and demolition phase.

It is believed the protesters targeted the Thameslink portion of the combined project where Crown House is the main M&E contractor.

Police were called to break-up the dispute.

At another protest in Newcastle sparks tried to block a construction site near the Tyne Tunnel.

A Tyne Tunnel spokeswoman said: “A peaceful protest of up to 20 people gathered at the construction site entrance in East Howdon, rather than at the Tyne Tunnel itself, which is almost half a mile away.

“There were no traffic impacts from this, and the tunnel certainly had no threat of blockage. There was no police involvement at the Tyne Tunnel site.

One rank-and-file leader promised more strikes and “civil disobedience” as electricians protest against plans by the major M&E contractors to pull-out of the JIB agreement