The reports passed to police raise very serious concerns about potential criminality around the union’s development project.

The 170-room hotel and conference centre was built under the leadership of former general secretary Len McCluskey and completed in December 2020.

Construction costs for the 170-bed Unite Hotel, regional office and conference centre, soared from around £57m to £98m.

Subsequent independent property valuations are understood to value the property at around £30m.

After taking over from McCluskey in 2021, now general secretary Sharon Graham commissioned Martin Bowdery KC to investigate the union’s vastly over-budget Woodcock Street development.

A spokesman for Unite said: “The newly-elected general secretary of Unite pledged to find out if there was any wrongdoing in the construction and spending related to the Birmingham Hotel and conference centre.

“True to her word, after her election, Sharon Graham, commissioned an independent KC inquiry into the Birmingham development and later a separate inquiry and external forensic investigation into Unite’s affiliated service providers.”

He added: “Due to very serious concerns about potential criminality that have emerged, both these reports are now being shared with the police.

“The police have requested that Unite does not release the contents of the reports while they are conducting their inquiries. While these are ongoing Unite will not be making any further comment.

“The general secretary is committed to doing all in her power to recoup any monies lost, by all means necessary and holding anyone responsible to account. It is clear this transparency would not have happened without the determination of the general secretary to ‘leave no stone unturned’ to get to the truth”.