The Office of Fair Trading may launch criminal proceedings against directors if the construction industry does not co-operate with its investigation into cartels in the sector.

So far, the OFT has used only civil powers, but said it was considering criminal investigations, which carry up to five years’ imprisonment, and director disqualification for “dishonest” individuals. So far no directors have been disqualified.

Deborah Jones, deputy director of the cartels group, said: “We haven't yet used criminal powers, but will if we detect dishonesty.”

The inquiry into cartels, which began in 2005, has uncovered more than 3,000 suspect contracts, worth £3bn.