Tory tensions over the European Union referendum have been laid bare again after George Osborne took a series of swipes at Boris Johnson over his backing for Brexit. The Chancellor accused the Mayor of London of campaigning for Brexit out of political ambition, and mocked his support for a Canadian-style free trade deal with the bloc.

Mr Johnson’s decision to play a leading role in the Leave team has infuriated David Cameron and Mr Osborne who believe he has acted opportunistically to court favour among Tory activists for a leadership bid.

The Mayor has retorted that he has a long history of criticising Brussels dating back more than 20 years when he was a reporter covering the EU.

Mr Osborne told BBC1’s Andrew Marr Show that Canada’s trade negotiations with the EU had so far lasted seven years and were still not complete.

He said: “I don’t want us to be Canada. I want us to be Great Britain. In the end this is not some political game. This is the biggest decision facing this country for 50 years.” In an apparent reference to his rival’s widely criticised appearance on the show last week, Mr Osborne said he would not “sit here and blather away and not actually do anything”.

What has the EU ever done for us? Show all 7 1 /7 What has the EU ever done for us? What has the EU ever done for us? 1. It gives you freedom to live, work and retire anywhere in Europe As a member of the EU, UK citizens benefit from freedom of movement across the continent. Considered one of the so-called four pillars of the European Union, this freedom allows all EU citizens to live, work and travel in other member states. What has the EU ever done for us? 2. It sustains millions of jobs A report by the Centre for Economics and Business Research, released in October 2015, suggested 3.1 million British jobs were linked to the UK’s exports to the EU. What has the EU ever done for us? 3. Your holiday is much easier - and safer Freedom to travel is one of the most exercised benefits of EU membership, with Britons having made 31 million visits to the EU in 2014 alone. But a lot of the benefits of being an EU citizen are either taken for granted or go unnoticed. What has the EU ever done for us? 4. It means you're less likely to get ripped off Consumer protection is a key benefit of the EU’s single market, and ensures members of the British public receive equal consumer rights when shopping anywhere in Europe. What has the EU ever done for us? 5. It offers greater protection from terrorists, paedophiles, people traffickers and cyber-crime Another example of a lesser-known advantage of EU membership is the benefit of cross-country coordination and cooperation in the fight against crime. What has the EU ever done for us? 6. Our businesses depend on it According to 71% of all members of the Confederation of British Influence (CBI), and 67 per cent of small and medium-sized enterprises (SMEs), the EU has had an overall positive impact on their business. What has the EU ever done for us? 7. We have greater influence Robin Niblett, Director of think-tank Chatham House, stated in a report published last year: “For a mid-sized country like the UK, which will never again be economically dominant either globally or regionally, and whose diplomatic and military resources are declining in relative terms, being a major player in a strong regional institution can offer a critical lever for international influence.

A new book serialised in The Mail on Sunday claimed Mr Cameron was “petrified” of Mr Johnson challenging him for the leadership, telling the former Deputy Prime Minister Nick Clegg that the Mayor is “clearly after my job”.

Asked about the book by the former Lib Dem cabinet minister David Laws, Mr Osborne replied: “I don’t think it’s the greatest … revelation in human history to discover Boris Johnson is interested in a job in government.”

The Prime Minister is also said to have confided in Mr Clegg that Michael Gove, the Justice Secretary, had “gone a bit nuts recently” and was driving him “around the bend”.

Mr Gove, who is one of six cabinet ministers to support Brexit, told a private meeting of Tory and Lib Dem ministers that plans to hold the referendum were “completely barmy”, the book claims.

The book, which has been written with Mr Clegg’s co-operation, is likely to open the former Lib Dem leader up to criticism after he recounts a talk with the Queen in which he outlined changes to the rule of royal succession.