By Peter Griffiths
LONDON (Reuters) - One of Prime Minister David Cameron's most senior advisors is to become Britain's new ambassador to the European Union, the government said on Wednesday, a role at the center of efforts to reshape ties with the EU before a possible in/out referendum.
Former finance ministry official Ivan Rogers, who advises Cameron on the EU and global issues, will be handed one of the toughest jobs in diplomacy at a historic moment in Britain's often tortured relationship with its biggest trading partner.
If re-elected in 2015, Cameron has promised to give Britons an EU membership referendum by the end of 2017, raising the prospect that the world's sixth largest economy could leave an organization it first joined in 1973.
A senior British diplomatic source said Rogers was "close to Cameron's thinking", adding: "It is going to be a very political role for the next three to four years."
The appointment of the Oxford-educated father-of-two was not universally popular.
Eurosceptics in Cameron's Conservative Party, a rebellious faction which has repeatedly challenged the prime minister's authority in parliament, pointed out that Rogers has worked for two of the biggest EU supporters in British politics.
He was once chief advisor to Ken Clarke, a Conservative cabinet minister who is one of the government's most vocal EU cheerleaders. He was also chief-of-staff to Leon Brittan, a former vice-president of the European Commission.
Former Europe Minister Denis MacShane said Rogers "knows Europe backwards" and is among the "crème de la crème" of British officials. He faces a daunting task.
"His job is to find more magic formulae than you'd find in a Harry Potter book to try and allow the prime minister of the day to sell what he wants to the British people," MacShane told Reuters.
The EU renegotiation could help decide if Cameron wins the next election in 2015 or whether he loses ground to the UK Independence Party, which argues Britain should leave the EU to shake off what it says is its stifling bureaucracy and meddling interference in everyday British life.
Germany and France have told Britain they will block attempts to cherry-pick from EU policy. However, Cameron is gambling on being able to reclaim some powers and wining allies for EU-wide reforms that can be presented as a British victory.
Rogers, an experienced civil servant who has held a succession of powerful jobs at the heart of government, will be crucial to that task.
He was in charge of former Labour prime minister Tony Blair's office and has been director of EU policy at the finance ministry. He has worked as Cameron's "sherpa" at G8 meetings, preparing the ground before leaders arrive for talks.
He also has private sector experience, having worked as the head of the public sector groups at Barclays Capital and Citigroup.
"I am honored to be appointed ... at this important time," Rogers said in a statement. He starts his new job in November.
He will replace Jon Cunliffe, who becomes deputy governor of the Bank of England.
Rogers' replacement as Cameron's Europe advisor will be Tom Scholar, who has worked as his G20 sherpa.
(Additional reporting by Paul Taylor; Editing by Andrew Osborn and Andrew Heavens)