Union sources said the 57-year-old victim was carrying-out piling work when the accident happened last week.

A spokesperson for Balfour Beatty said: “A serious incident occurred on our AWE Aldermaston site on 6 July 2023. As a result of the incident, a colleague has tragically lost their life.

“Our deepest sympathies are with our colleague’s family, friends and co-workers at this time.

“Works have since stopped as we support the authorities with their investigation. As these are ongoing, it would be inappropriate to comment further.”

Balfour is building a new laboratory and office complex for AWE at the nuclear warhead research centre.

An AWE spokesperson said: “On the evening of 6 July, there was an incident on a construction area within the AWE site at Aldermaston involving Balfour Beatty employees, one of whom was airlifted to hospital. It has now been confirmed that this person has tragically passed away. Our thoughts and deepest condolences are with his family, loved ones and colleagues.

“The event did not involve any of our nuclear installations or any nuclear materials. There is no risk to the public.

“We are supporting our employees impacted by the events, and have stood up an incident team who will work with Balfour Beatty, the Office for Nuclear Regulation and Thames Valley Police to support the investigation that will now take place. As this is ongoing, it would be inappropriate to comment further at this time.

“We would like to take this opportunity to thank the emergency services for their response and care.”