The practice, called "cover pricing," is meant to keep companies on bidding lists, called tender lists. But cover pricing, done in collaboration with other companies, can also increase the prices of projects.

The investigation into illegal bidding practices began in 2004, The Times of London reported Thursday.

So far, 37 companies have applied for leniency, hoping for reduced fines, The Times reported.

A building association said the practice was not intended to gouge the public.

Chief Executive of the Construction Confederation Stephen Ratcliffe told The Times, "the only motive in these cases was to avoid doing the work but stay on tender lists and there was no intention to make a single penny at the tax payers' expense."