Site sources contacted the Enquirer claiming that a spate of deaths had sparked safety fears across the delayed station job.

It is understood the first two deaths earlier this year were recorded as heart attacks.

The latest deaths are believed to have occurred last Saturday and on Monday night when two Crossrail workers also died in their sleep at home.

The site source said: “Alarm bells are ringing among the workforce about this.

“None of the lads were that old – the oldest was in his fifties.”

The Enquirer understands the issue has been raised with main contractor Costain Skanska Joint Venture (CSJV).

Workers have previously downed tools on the site following concerns over dust levels.

The source said: “The lads are very upset and nervous about this and want this to be properly investigated to find out exactly what is going on.”

CSJV has been contacted for a comment.