OFT senior director of cartels and criminal enforcement Simon Williams warned that cartel activity could even apply to the public sector and school-building projects.

He said: “Cartels are not the preserve of big business - for example, if a local authority needs to find a contractor to refurbish its schools, it is unacceptable for local contractors to seek to rig the tender process by colluding on price. That's bad for taxpayers, consumers and other businesses.”

Williams added that whistleblowers will be well-rewarded. He said: “We believe that it is in the public interest to offer financial incentives in the hope that it will encourage more people who have good information about the existence of hard core cartel activity to come forward, and in exceptional circumstances these incentives may be as high as £100,000.”