The union has been involved in a long running dispute with the contractors over worker representation on the job where it said Unite officials are not allowed “to freely speak to workers during their breaks in its welfare facilities.”

Recent alleged accidents include a worker suffering arm injuries after clay fell from height onto them, a lorry overturning into a ditch, a skill saw blade came off its mooring, a hammer breaking a worker’s wrist and a digger bucket hitting a worker’s foot.

Unite national officer for construction Jerry Swain said: “Workers operating on the Costain/Skanska/Strabag joint venture, will be rightly worried and concerned for their safety.

“This project is crying out for union safety reps who play a unique role in protecting workers and preventing accidents.”

An HS2 Ltd spokesperson said: “The safety of our workforce and the public is HS2’s number one priority. We have an open and transparent reporting culture, and all health and safety incidents are fully investigated, key learnings and actions for HS2 and our contractors identified, and these are then shared across the project.

“All those who work on HS2 have the right to go home unharmed, and we continue to work with and challenge our contractors to provide the highest levels of health and safety standards.”

An SCS JV spokesperson said: “The health and safety of our teams and the public is always SCS’s first priority and we have offered Unite access to our sites, which exceeds levels usually seen across the industry.

“This enables them to meet our team at inductions, work sites and our welfare area. We first offered this to Unite in 2018 and on numerous occasions since.

“We continue to make contact with them to reiterate this offer as we seek to maintain an open dialogue with Unite and to allow them to carry out their activities.  To date they have not taken up this offer, however it remains open to them.”