David Cameron and Nick Clegg renew their vows an in attempt to draw a line under weeks of Coalition infighting

David Cameron and Nick Clegg today attempted to draw a line under weeks of Coalition infighting with a public show of unity and a pledge to see the Government through to 2015.

The Prime Minister said he was “even more committed” to the Coalition than he was when it was formed two years ago and insisted there was still a “huge momentum” in Government.

He announced that two parties would be publishing a “mid term review” later this summer setting out their priorities for the next two years.

The two men were speaking at an event in Birmingham where they announced details of new investment in Britain’s rail infrastructure.

They unveiled a £9.4 billion package of rail projects, including £4.2 billion worth of new schemes, will include the electrification of the main rail route between London and Sheffield and upgrades to stations and tracks to create capacity for an additional 140,000 daily rail commutes at peak times.

Later this week George Osborne is expected to announce new measures to allow the Government to increase infrastructure spending by using the Government’s favourable credit rating.

There is likely to be an emphasis on house building which ministers have identified as a reasonably quick and cheap way of stimulating growth.

With Parliament rising for the summer recess tomorrow Government strategists are hoping to regain the initiative ahead of the break and put behind then several difficult weeks.

Mr Clegg dismissed the row over Lords reform as a “bump in the road” and said despite disagreements between the two parties “none of that will stop us from continuing to govern in the national interest for the country.”

Mr Cameron admitted questions had been raised about the future of the Coalition in the wake of the Tory rebellion last week over House of Lords reform.

But he added: “I just want to say I am even more committed to coalition government, to making this coalition government, today than I was in May 2010 when Nick Clegg and I formed this government.

“I believe it has real purpose, a real mission.”

Mr Mr Clegg acknowledged that they disagreed on some issues but on the big themes of growth, education and welfare reform they were as one.

“We are two different parties: he doesn't agree with all my opinions and I don't agree with all his opinions. That's coalition government,” he said.

"It's tough also to be in government in difficult times. It is not always a walk in the park or in the rose garden.

"We need to put short-term popularity to one side and get on with making the big long-term reforms and changes that this country so desperately needs," he said - identifying those areas as economic and social renewal.

Mr Cameron said that in two years there had been only "one or two episodes like last week" and that the major revolt did not reflect deeper problems within the coalition.

"You always have bumps and scrapes and difficulties along the way. That is the nature of politics," he said.

"With the House of Lords you always have to be frank: there are people on both sides of the argument, people of principle. Some of them have held their views either for or against having elected members for a very long time.

"So I do not take that as an indicator of the health of the Government or its momentum or its purpose. I think it has real purpose, real momentum and that is what we are committed to driving forward in the years ahead."

There was "much more to come" on the shared agenda, he But despite the show of unity Coalition tensions were underlined by renewed calls from Liberal Democrats for Mr Cameron to deliver on Lords reform and demands from Tory MPs for him to take a tougher stance against Mr Clegg's party.

Graham Brady, the chairman of the Conservative backbench 1922 Committee, said he believed the coalition was "very likely" to end before the general election, set for 2015.

"I think it would be logical and sensible for both parties to be able to present their separate vision to the public in time for the public to form a clear view before the election," he said.

He added: "Of course, it is always possible that that moment of separation could come sooner. It's very difficult to predict when that might be."

The former Defence Secretary, Liam Fox, reflecting the feelings of many Tory backbenchers, said that his party had a "particular problem which is the Liberal Democrats". He said: "What I think they have to remember is that they are a sixth of the Coalition, not half the Coalition."

Meanwhile the Liberal Democrat Energy Secretary, Ed Davey, called on Mr Cameron to ensure his backing for the Lords reform plans. "The Coalition Agreement isn't a pick-and-mix agreement, you've got to deliver on all of it. We're expecting the Prime Minister and the Conservative Party to deliver on the Coalition Agreement."

And the former Liberal Democrat leader, Sir Menzies Campbell, warned that the party's MPs might "find it very hard to swallow" the proposed boundary changes unless Lords reform goes ahead.