Vow renewal to show there's life in coalition yet

David Cameron and Nick Clegg will plot a course towards a potential extension of their coalition tomorrow, when they present a "mid-term report" on their performance in government since 2010.

The Prime Minister and Deputy Prime Minister will detail their "key achievements" at the parliamentary mid-point, in areas including the economy, jobs, welfare and health.

Mr Cameron last night underlined his determination to serve as Prime Minister until at least 2020 to oversee a wave of new reforms, including a renegotiation of Britain's relationship with Europe.

In an interview with The Sunday Telegraph, he said there would be no turning back on policies unpopular with his party's grassroots, such as same-sex marriage, the imminent child benefit cut for the better-off and the protection of foreign aid spending.

Asked if he would stay as Prime Minister until 2020, amid rumours that he would stand down and cede the floor to challengers including London's mayor, Boris Johnson, Mr Cameron said: "Yes – look, I want to fight the next election, win the next election and serve – that is what I want to do."

The mid-term event, revealed in The Independent on Sunday in October, will also be used to bring the Conservatives and the Liberal Democrats closer together as they go into the second half of the parliament – and the election beyond. Officials last night said the restatement of vows, after a troubled period distorted by arguments over issues such as the House of Lords and Europe, was an opportunity to stress that "both parties remain committed to the Government's programme of economic and social reform".

Mr Cameron and Mr Clegg are also expected to "make a political argument about the coalition", challenging the claim that "the coalition has been a single-issue government, focused on nothing but the deficit".

But Labour's vice-chairman, Michael Dugher, said: "They said they'd fix the economy. But living standards are still falling for the hard-working majority, while a handful of millionaires get huge tax cuts. They said they'd fix welfare, but the welfare bill has gone up not down. Families who put their trust in David Cameron and Nick Clegg's promises of change will be bitterly disappointed to see that another relaunch is all they are offering."

The coalition 2.0 agreement had been shelved last year as the Tories and Lib Dems squabbled over a number of contentious policies – and Downing Street advisers fretted over whether they could fill it with inspiring new ideas. But in the autumn, responsibility for drawing up the roadmap to 2015 was handed to a close group of five leadership "trusties": Cabinet Office ministers Oliver Letwin and David Laws; the Chief Secretary to the Treasury, Danny Alexander; Lib Dem special adviser Julian Astle, and Tory aide Patrick Rock.

The PM and his deputy will publish the document and announce forthcoming policy areas tomorrow at a joint event in London following a morning meeting of the Cabinet. The mid-term review will "highlight key achievements of the coalition and set out some new policies for the rest of the parliament".

The party leaders are expected to state that the Government will continue to prioritise fixing the economy and reforming welfare and education, but the mid-term review will also "outline additional long-term policy challenges that we want to tackle in the second half of the parliament".

"Key achievements" listed in the document include moves to "cut the deficit left by Labour by 25 per cent and set out credible plans for a balanced budget"; to create "over a million private-sector jobs as the economy rebalances, and a record number of apprenticeships"; and to make "welfare fairer".