David Cameron has picked journalist Camilla Cavendish to head the Downing Street policy unit as he reshapes his top team.

The Sunday Times associate editor and columnist, a contemporary of the Prime Minister's at Oxford University, wrote recently that an opt out from freedom of movement "must be a red line" in negotiations over the UK's relationship with the European Union.

She replaces MP Jo Johnson who was made Cabinet Office minister in the post-general election reshuffle.

Recently featured as a panellist on the BBC's Question Time alongside Ukip leader Nigel Farage and comedian Russell Brand, she was the author of a 2013 Government-commissioned review that recommended minimum training standards for NHS healthcare assistants.

"Delighted to be heading Downing Street Policy Unit. A great honour," she wrote on Twitter.

Care Quality Commission chief executive David Behan said she brought a "sharp intellectual challenge" to the organisation and was sorry to have to lose her from its board.

The Spectator magazine reported that much of the team would remain in place - with Ed Llewellyn staying on as chief of staff but devoting a lot of time to the EU renegotiation.

That means extra responsibility for spin chief Craig Oliver, who is handed more of a policy role as political and communications director.

In a post-election column, Ms Cavendish suggested the crisis in the eurozone could present the PM with an opportunity to "negotiate a new, subsidiary membership in a two-tier EU, with the warning that we might leave unless we get it".

A Greek exit could require treaty change in Brussels to beef up the European Central Bank, she suggested, handing the UK a prime opportunity to secure concrete changes.

"The Government now has a clear mandate to conduct a tough renegotiation with the EU in which an opt-out from freedom of movement must be a red line."

She also called on Mr Cameron to bring together a group of eurosceptic politicians "savvy and trusted on the right" - including former cabinet minister Owen Paterson and backbencher Jacob Rees-Mogg - to help push forward the agenda.

She warned Mr Cameron that his administration "faces a real and present danger from its backbenchers unless Cameron can embrace MPs he has previously left out in the cold".

Mats Persson, director of the think tank Open Europe, will serve as Mr Cameron's adviser on EU reform, Downing Street has confirmed.

The Swedish chief of the pro-reform think tank will work alongside the No 10 policy unit.