Workers have also been in touch with the Enquirer to complain about site conditions including claims that on some parts of the job there is a one hour walk to the nearest toilets.

The 500 strong team of M&E workers are angling for an extra £10 an hour on top of current wages for the scheduled 70 weeks remaining on the project.

Contractors are looking to recruit hundreds more electricians to complete the fit-out of the tunnels and stations.

But one source among the rank-and-file workers said: “There’s just not the qualified workers around and we just can’t see how it will be ready on time.”

It is understood the skills shortages are causing tension between Crossrail and contractors who are also concerned about the potential for industrial relations problems.

Crossrail chiefs are adamant the project is on-time and on-budget.

The job is now 75% complete with half the permanent track now laid.

Another electrician said: “All the track is supposed to be down by Christmas but I can’t see that happening.

“Not having track down has huge knock-on effects.

“We have to walk miles to the work sites and up to an hour to the nearest loo during shifts.”

A Crossrail spokesperson said: “The Crossrail programme is over 75% complete and is being delivered on time and on budget.

“Our contractors remain confident that they and their supply chains have the skills and resources in place to continue the successful delivery of the project.”