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Downing Street has denied the deputy prime minister's claim David Cameron was kept in the dark about Michael Gove's plans to scrap GCSEs in England.

Nick Clegg told ´óÏó´«Ã½ News neither he nor the prime minister knew of the proposal until they read it in .

But No 10 sources said the PM did know the details but said they had not been submitted for formal government discussion.

A Downing Street source described the leak as unhelpful.

Sources close to Nick Clegg said: "I doubt very much the details of the plans revealed in the Daily Mail were known much outside Michael Gove's private office."

Mr Clegg said the prime minister had not been told about his Conservative colleague Mr Gove's proposals in advance - and he suggested that the idea could not go ahead without the support of the Lib Dems.

"This has not been subject to a collective discussion in government. Neither myself nor the prime minister were aware of it," he told ´óÏó´«Ã½ Radio 4's World at One programme.

"That's self-evidently the case. And if Michael Gove wants to turn some of his ideas into government policy he's entirely entitled to put that forward for wider discussion.

"By definition in a government if you have collective agreement, and particularly in a coalition, it requires support from all sides."

Senior Lib Dem Lord Oakeshott described Mr Gove's announcement as a "political stunt" which stood no chance of becoming a reality as his party would block it.

"This is Michael Gove starting his campaign for the leadership of the Conservative Party several years early," he told the ´óÏó´«Ã½'s Daily Politics.

If Mr Gove's plan goes ahead, students would begin studying what the leaked document says will be "tougher" O-level style exams in English, maths and the sciences from September 2014. They would take their exams in 2016.

Less academic pupils would sit a different "more straightforward" exam, like the old CSE.

The ideas, if introduced, would amount to the biggest change to the exams system for a generation.

Speculation is rife at Westminster about the source of the leak, with some, including ´óÏó´«Ã½ This Week presenter Andrew Neil, suggesting it came from the education secretary himself.

Justice Secretary Ken Clarke, speaking on ´óÏó´«Ã½ One's Question Time, suggested the leak could have come from within the educational department.

"If the secretary of state for education leaked it I would feel very strongly about it, but I don't think he did," he said.

"This has been worked up in the Department for Education, as I understand it, and when it's finished it will then go to a cabinet committee, which actually the chairman is Nick Clegg and the deputy chairman is me and it will be considered collectively."

He backed some parts of the proposed policy, such as stopping exam boards competing against each other and giving apprenticeships "proper status".

But he added: "What will happen is it will come to a committee which he [Nick Clegg] chairs and I doubt it will come in exactly the form in the Daily Mail. It is a policy being worked up inside the department."

Andy Burnham, for Labour, criticised Mr Gove's proposal as "elitist" and accused him of wanting to turn the clock back to the 1950s.

Explaining his plan in the Commons on Thursday, Mr Gove said the current exams system needed to be improved.

"Children are working harder than ever but we are hearing that the system is not working for them. We want to tackle the culture of competitive dumbing down."

He said rigour needed to be restored to the system if England was to keep pace with educational improvements in some other countries.

The Education Minister for Wales, Leighton Andrews, has said Wales will not return to O-level-style exams.