Labour supplier Hennelly’s, which went into administration earlier this month, owed more than £1m to creditors when it collapsed.
The scale of the debt was revealed by administrator Hurst Morrison Thompson, which has made 90 redundancies at the firm since it went into administration on 3 July.
The company was working on three contracts, including some for Balfour Beatty and Metronet. Two were terminated immediately, but the third is being completed by a skeleton staff of 10 employees.
Hennelly’s’ employees walked off Balfour Beatty’s King’s Cross Northern Hall ticket office earlier this year, claiming they hadn’t been paid for four weeks.
Director Sean Hennelly is said to be looking at options to keep the company afloat. A Ucatt spokesman said: “If they did try to re-emerge, we would work very strongly with contractors to urge them not to use them.”