David Cameron has denied that “tough” decisions on spending will mean cuts to frontline health services while campaigning in marginal seats he needs to win to secure overall victory.

The Tory leader said the squeeze on spending would be worse than for many years - and would mean more cuts than identified so far - but insisted he would not allow it to affect those in need.

And he suggested reforms would draw on private sector cost-cutting in firms such as Tesco as he answered questions at a store alongside the supermarket giant’s boss Sir Terry Leahy.

Buoyed by opinion polls showing a Conservative lead just four days ahead of polling day, Mr Cameron resumed his frenetic tour of the UK with visits to Liberal Democrat and Labour heartlands.

In Newquay, Cornwall, he told business leaders that the Liberal Democrats - who hold several Tory target seats in the area - had been exposed as having “crazy” policies, notably on immigration.

And campaigning in Delyn, Wales, where the Tories need a swing of nearly 10% to unseat Labour’s police minister David Hanson, he accused Gordon Brown of resorting to “scare” tactics.

He repeated his pledge to act “in the national interest” in the event of a hung parliament but warned it was most likely to result in a “muddle” that left Harriet Harman or Ed Balls running the UK.

In an interview for BBC1’s The Andrew Marr Show, he said the Institute of Fiscal Studies was wrong to say that a Conservative government would have to find a further £52bn in spending cuts but accepted they would be more extensive than publicly detailed so far.

“There are undoubtedly going to be some very difficult and tough decisions,” he said - insisting he had “no plans” to raise VAT.

“It isn’t possible to explain everything that has to be done from a position of opposition,” he added when pressed for more details of where the axe may fall.