Sky News has revealed tonight that Rohan Silva, one of the Prime Minister’s key advisers, is leaving Downing Street. Silva might not be a household name but he has been a hugely influential figure there these past few years.

In opposition, he worked for George Osborne before moving to work for David Cameron in government. He has been the driving force behind spending transparency, Tech City and crime maps. There have been few more pro-enterprise and pro-reform voices in this government. His departure is a big blow to Tory radicalism.

One of the things that marked Silva out was a thirst for new ideas that is all too rare in British politics. He was the man who got the Cameroons interested in behavioural economics—Nudge and all that—and has kept a steady tide of intellectual and thinkers flowing into Number 10.

There’ll be much speculation about why Silva is leaving. Already, tonight commentators are chalking it up to a lack of radicalism in Number 10, the state of the Cameron operation or the stultifying influence of the civil service. But Silva has been keen to go and start a business for years now—hence, the earlier, erroneous reports of his departure. The surprise shouldn’t be that he’s leaving but that he has stayed so long.

Tags: Coalition, Conservatives, David Cameron, Downing Street, Number 10, Rohan Silva, UK politics