Mr Willetts will be paid pounds 25,000 a year by Monitor for around half-a- day's work a fortnight, he said yesterday. He will add this to his other part-time post that he gained in June, that of economic adviser to Dresdner Kleinwort Benson, the German-owned investment bank.
Monitor was founded in Boston in 1983 by graduates of Harvard Business School, and most of the firm's 800 staff are still based in that city, with 100 in London.
Richard Rawlinson, a spokesman for Monitor, said: "We advise mostly large multi-national companies on competitiveness issues. We see Mr Willetts helping us on the organisational parallels between governments and businesses. It will basically be a research job. He will also sit on Monitor's Eurasian Board of Advisers."
Mr Willetts said: "They approached me, and they seemed to be be very sophisticated analysts of business strategy. I hope to be working with specific clients, but it's early days."
Mr Willetts quit as a minister last autumn immediately after the publication of a report in which he was sharply criticised by the Tory-dominated Standards and Privileges Committee which examined the allegation that he attempted to subvert a parliamentary inquiry into the Neil Hamilton "cash-for-questions" affair.
Mr Rawlinson said the fact that Mr Willetts had resigned from the previous government had not affected Monitor's attitude to him: "We're interested in his intellectual qualities. He's respected as one of the best thinkers around today."
Mr Willetts is also a former Whip who has had a considerable influence over strategic policy-making in the Conservative party over the last 10 years. He was consultant director of the Conservative Research Department from 1987 to 1992.
A graduate of Christ Church, Oxford, he began his career in the civil service and was a Treasury official from 1978 to 1984. He went on to become a member of the Downing Street Policy Unit for two years. Then, for five years, he directed the Centre for Policy Studies.