The Consort consortium of Balfour Beatty, Morrison Construction and the Royal Bank of Scotland won the contract to build and operate the Edinburgh Royal Infirmary (ERI) in 1996.

The deal is due to run until 2028. But health chiefs at NHS Lothian are threatening legal action after patients lives were put “at risk”.

Surgeons had to finish a recent operation by torchlight after maintenance workers cut power to the theatre.

Alan Boyter, executive director of NHS Lothian, told The Scotsman: “We are consulting our lawyers to discuss what options we have in relation to the contract.

“We have reached the point where we can no longer tolerate the repeated, serious and potentially life-threatening nature of these incidents at ERI by our PFI provider Consort.

“Patient safety is always our absolute priority and we will not allow that to continually be put in danger by a third party.

“We are angry and frustrated with the performance of our PFI provider Consort.”

Responding to the theatre blackout incident, Stephen Gordon, director of Consort, said the power had been disrupted for around ten minutes.

He said: “Consort has taken this incident very seriously and have undertaken a thorough investigation into this matter in conjunction with NHS Lothian to review the current operating procedures in place for works of this nature.”