Private sector tax experts prepared to switch sides and divulge their know-how to the Revenue have become the latest weapon in its battle against aggressive tax avoidance.

Dave Hartnett, permanent secretary for tax at Revenue & Customs, recently told a group of lawyers that it had learned a lot from recruiting bankers and lawyers who had been made redundant in the credit crunch. He said the Revenue welcomed their knowledge although it did not ask for any information about their past work.