Sainsbury’s has sent letters to contractors in its supply chain asking them for assurances that bid rigging has been stamped out.

It is understood that the supermarket chain has acted in a similar way to public sector clients by issuing an immediate call to contractors following the allegations made against the construction industry.

A source said: “The very first letter I got after the Office of Fair Trading’s announcement was from Sainsbury’s. I suppose they want to be whiter than white given their own problems with the regulator.”

The chain was recently accused of fixing tobacco prices. It also admitted sharing information on dairy prices in December last year.

Sainsbury’s declined to comment.