Minister of state, Cabinet Office UP 18

Oliver Letwin may not have much of a public profile these days, but this invisibility shouldn’t be mistaken for diminishing influence. Indeed, the opposite is true.

He is the only generalist in the top 10 of the HSJ100 - big guns such as the prime minster, chancellor of the exchequer and deputy prime minister are all excluded from consideration. Mr Letwin’s official role is minister of state in the Cabinet Office, a post he has held since May, when he played a pivotal role in the coalition negotiations. But his influence far outweighs any titles. He is one of the trusted inner circle, having been an early supporter of David Cameron’s leadership bid in 2005. Indeed, across 30 years in the Conservative party, he has had a colossal impact.

Some even talk of Mr Letwin as the latest incarnation, or at least the equivalent, of Sir Keith Joseph, the “power behind the throne” in the creation of Thatcherism. In the early 1980s Mr Letwin actually worked for Sir Keith. Since becoming an MP in 1997, he has held a number of briefs, notably shadow chief secretary to the Treasury, shadow chancellor and shadow economic affairs secretary. Between 2005 and 2010 he was chairman of the party’s policy review and chairman of the Conservative research department, charged with, among other things, drafting the election manifesto, attempting to marry Tory traditions with the modern world.

Mr Letwin is credited with much of the fundamental thinking behind the big society. He has been a key driving force behind encouraging greater plurality of provision - from the private and third sectors - and the development of new ownership models. It is in his work to reposition the Tory party, to appeal to new voters and to solve new problems that this reserved figure can be thought of as the conscience of the Cameroonian reforms. In The Daily Telegraph’s recently published list of the top 100 most influential right-wingers Mr Letwin polled higher than Andrew Lansley.

The great challenges for this coalition government are still to come. It will have to hold the line on the elimination of the structural deficit, which is going to be incredibly tough. At the same time, Andrew Lansley is instituting historic reforms to the healthcare system. It doesn’t take a soothsayer to see that the NHS is in for a bumpy ride. Informed opinion among policy wonks is that some of the changes outlined in the white paper, such as GP commissioning, are likely to generate a greater deficit, burning more money, not less. Even the government’s commitment to increase spending will soon feel like a decrease. The unions will go berserk.

As the Treasury gets frustrated with Richmond House for provoking a media storm about the health service - on which the Conservatives worked so hard to detoxify their image - and for burning up economic and political capital, and as Number 10 starts to get jittery as well, Mr Cameron will need someone he trusts, who can keep a level head under pressure. He’ll probably want to phone a friend - a clever friend with a Big Brain at that, with a big picture view of policy. Mr Letwin, a believer, may be called on to balance some of the tensions, a task he would do very well.

Nick Seddon, deputy director, Reform