Nick Clegg has predicted 2015 will see the “first full blown scarcity election” as he set out how the Lib Dems would seek to occupy the centre ground between Labour and the Conservatives.

The Lib Dem leader told journalists in Westminster on Thursday that all thee main parties would accept “shared assumptions” about the level of spending cuts, but the debate would be about what to cut and when.

Clegg’s analysis was shared by David Miliband on Monday, who fuelled rumours of his return to the Labour front bench when he said he accepted the overall level of cuts to benefit payments needed.

“The Government have projected the cost of all benefits, all tax credits and all tax reliefs,” he told MPs. “I am happy to debate priorities within that envelope. A proper debate – about choices not the total sum.”

Clegg anticipated the 2015 campaign would be a “quite gritty realistic weighing up of options” rather than the “frothy happy-go-lucky” atmosphere of past elections.

And summing up the Lib Dem’s core centrist campaign message he said he hoped to convince voters that: "Labour can't be trusted with money, the Tories can't be trusted with society."

Clegg also addressed the debacle of the Lib Dem’s promise not to ever vote for any increase in tuition fees. He said the 2015 manifesto would be “stress tested” for deliverability as well as desirability. “We are not going to make that mistake again,” he added.

The party’s manifesto, which will be written by David Laws, will repeat the practice of having “front row commitments” on the front page that the party would deliver in government “come Hell or high water”.

In any coalition negotiations in the wake of an inconclusive 2015 election, the Lib Dems would refuse to budge on these pledges, but would be prepared to compromise or drop other policies on the inside pages. He suggested both Labour and the Conservatives produced their manifestos in a similar manner.

Following the row over tuition fees, which severely damaged the party’s standing with its supporters as well as causing internal party fury, the Lib Dem leadership sought to point out that the pledge was not actually on the front page of the 2010 manifesto.

However that reasoning did not wash with most, meaning Clegg, Laws and their colleagues will likely make this distinction more explicit in 2015.

Asked if he would definitely contest the next election Clegg replied: “Of course I’ll stand in 2015”. However he would not be drawn on whether, like David Cameron, he intended to remain leader of his party until the following election in 2020.

The Lib Dem leader also repeated his support for the TV debates. When asked if Nigel Farage should be allowed on the platform alongside him, David Cameron and Ed Miliband, Clegg grinned before replying: "I think the format we had before was a good one".

Earlier on HuffPost: