Graham Brady MP

David Cameron and Nick Clegg have stressed their commitment to the Coalition amid fresh hints of an early split.

In a speech in the West Midlands today, the Prime Minister claimed he was now more committed to the alliance than he was two years ago, and revealed that a mid-term review would be published this summer.

Appearing alongside the Deputy Prime Minister, Mr Cameron insisted the Coalition had "a real purpose and a real mission", and suggested it would last for the full term of five years.

"I am even more committed to Coalition Government today than I was in 2010 when Nick Clegg and I formed this Government," he said.

"It’s vital this Government has the majority, the decisiveness and the strength to cut our deficit - which we’ve done by a quarter in two years - and to have all the drive in the year ahead."

The Lib Dem leader also stressed his commitment, saying the reasons for the Coalition were "as strong today, if not stronger" than they were in 2010.

Mr Clegg said the mid-term review would be "a good reminder of quite how much we’ve done, packed in, over two years and how much we’ve got left to do".

This morning Boris Johnson became the second senior Tory in as many days to hint at an early Coalition split, telling the BBC his party would part company with the Lib Dems "at some stage before 2015".

His remarks come after the chair of the 1922 Committee, Graham Brady, said the Coalition was likely to end before 2015.

“Logically it must be true that at some stage before 2015 there will have to be a decision to part company and campaign on different perspectives," the London Mayor said.

"The Liberal Democrats will have what they want to say to the country and we the Conservatives will have what we want to say to the country. Of course that’s absolutely natural."

However Mr Johnson insisted the Coalition was a "marriage doomed to succeed" until that point.

Mr Brady told the BBC's Westminster Hour last night it would be "logical and sensible" for the two parties to talk about splitting up to a year before the election.

The backbencher was one of the 91 Tory rebels to vote against the Coalition plans for Lords reform, and said the parties could present a "separate vision" to the public.

Tory MP Stewart Jackson welcomed the leaders' joint appearance, but warned the Lib Dems the Coalition "will be dead" if they "renege on their solemn undertaking" to support boundary reform.

"If they renege on that particular arrangement then I can only see that the Coalition government will be dead. And we’ll move then to a supply and confidence, or a Conservative minority government," he told BBC News.

David Cameron yesterday narrowly won a vote, 168 to 118, to change the rules of the influential 1922 committee of backbenchers to allow government MPs to take part in all its votes. The move has caused unrest on the Conservative backbenches, some of whom accuse Cameron of curbing internal party democracy.