Steve Hilton's next Big Idea: Swap Downing Street for time out in California

The Prime Minister's most influential adviser, Steve Hilton (pictured), has announced his departure from Downing Street (Getty Images)

He is credited as the architect of the Big Society and once suggested the abolition of paid maternity leave. Now Steve Hilton, David Cameron's most influential adviser, has pulled off one last surprise: unexpectedly announcing his departure from Downing Street for an unpaid academic job in California.

Although he intends to return to No 10 in the summer of 2013 after a year's sabbatical at Stanford University, some Conservative insiders believe that he is unlikely to come back to his present role.

Mr Hilton is famous for his "blue skies thinking" and padding around Downing Street in socks and a T-shirt. He is one of Mr Cameron's closest friends but has found government frustrating. He has complained privately about the obstacles to putting his ideas into practice thrown up by the civil service, the Liberal Democrats and the European Union and was dismayed to see the health reforms watered down.

His departure is a surprise, because he has always urged Mr Cameron to make use of every minute of his scheduled five-year term to secure lasting change in case he loses power at the next election.

He has often clashed with the Chancellor George Osborne, who believes the Tories' priority should be to win an overall majority in 2015 rather than risk losing public support by pursuing unpopular reforms.

But No 10 sources denied that Mr Hilton is leaving because of strained personal relationships with rival advisers who also seek to influence the Prime Minister. "He has been at his happiest in the past three or four months," one said. Mr Hilton returned to Mr Cameron's side after a previous long break in California while the Tories were in opposition. His wife, Rachel Whetstone, is Google's communications chief and is returning to the US.

A Downing Street spokesman said: "With his wife and young family, Steve will be moving to California. He will spend his year on campus teaching, researching and writing, and will focus on innovation in government, public services and communities around the world."

Mr Hilton is the architect of Mr Cameron's flagship Big Society policy and his absence will fuel speculation that it is being downgraded. He will not be replaced and his duties will be shared between several staff. One option is for him to return to Conservative HQ to run the party's 2015 election campaign.

Some colleagues have found the impatient, irrepressible Mr Hilton difficult to work with – but even his enemies admit that Downing Street will have less of a creative spark without him being there.

Blue-sky thinking: Hilton's hits

Big Society

The cornerstone of Mr Hilton's philosophy and the ideological underpinning to Project Cameron. At least one relaunch and several personnel changes later, some senior ministers have gone cold.

Fly Branson

Mr Hilton recently advised Education Secretary Michael Gove to abandon the "fat cats" of British Airways when travelling abroad and use "upstart" Sir Richard Branson's Virgin.

Hug a husky

Mr Hilton persuaded Mr Cameron to go to the Arctic Circle for a photo shoot with a group of huskies to prove the Tories' "Vote Blue, go Green" credentials.

Get the economy moving by...

Abolishing Jobcentres and paid maternity leave along with suspending consumer-rights legislation for nine months. This was part of a blueprint to boost the output of UK PLCs.

Literal blue-sky thinking

While in opposition, Mr Hilton is said to have floated the idea of acquiring cloudbusting technology to turn Britain's grey skies to his favourite political hue.

Cahal Milmo