Mr Aitken will head a policy task force for think-tank the Centre for Social Justice, which advises David Cameron on social issues.

The appointment is likely to be seen as a remarkable comeback for someone who was jailed for 18 months in 1999 for "calculated perjury" during a libel action.

Mr Aitken resigned as Chief Secretary to the Treasury two years earlier so he could sue the Guardian over allegations that a Saudi businessman had paid for him to stay at the Paris Ritz in breach of ministerial rules.

Launching the action, he notoriously insisted that the "simple sword of truth" would help him win.

Speaking to the Observer, the 65-year-old confirmed he would be heading the study for the CSJ.

"It is a cause dear to my heart for obvious reasons," he said. "It is an assignment well worth taking extremely seriously. This isn't an ego trip for me. This is a job to be done. I have a very good team who I think will help to do it well."

Former Tory leader Iain Duncan Smith - who runs the think-tank - is to unveil the appointment formally on Monday.

Mr Duncan Smith told the Observer it was time to rehabilitate Mr Aitken, who conducted numerous confessional-style media interviews after leaving prison - where he claimed to have rediscovered the Bible.

"Everybody deserves a second chance, that is the whole philosophy of the Centre for Social Justice," Mr Duncan Smith said. "I am a profound believer in never writing people off. We are now using Jonathan's experience as a way of getting the most from him and him making a positive contribution to society."