The Conservative leader announced the proposals as part of a raft of measures that includes pledging to cut ministerial pay and end MPs’ subsidised food and drink if he gets into power.

Mr Cameron said he would require the Boundary Commission to set out detailed plans to reduce the number of MPs from 650 to 585, saving an estimated £15.5m a year.

In Scotland, this would mean a cut from 59 MPs to 53 with the probable creation of super-constituencies covering large swathes of the country.

Last night John Robertson, Labour MP for Glasgow North West, criticised the move as an attempt to negate the party’s electoral unpopularity north of the border.

He told The Herald: “It’s a numbers game he is playing to make sure the big English vote outweighs the Scots and the Welsh.

“It is another nail in the Conservative coffin in Scotland. I would fight this the best I could.

“If they were to win an election with a majority then they could bring it through if they wanted, but I think he might hit a lot of obstacles within his own party.”

Alistair Carmichael, LibDem MP for Orkney & Shetland, said: “It will make vast chunks of the Highlands and Islands, and remoter parts of Scotland virtually unrepresentable. It is already difficult with constituencies like my own and the Western Isles. What David Cameron wants to do is build constituencies around numbers and numbers alone, and that’s got to be bad news [for democracy].”

While Mr Cameron admitted the £120m-a-year saving from his proposed measures was a “pin prick” in the giant £175bn budget deficit, he is hoping to steal a political march on Gordon Brown in the fall-out from the MPs’ expenses scandal by insisting his move shows leadership.

“With the Conservatives, the gravy train will well and truly hit the buffers,” Mr Cameron declared in a keynote speech in London.

The Tory leader also targeted Commons food and drink, saying: “Walk into a bar in Parliament and you buy a pint of Fosters for £2.10. That’s a little over half as much as in a normal London pub.”

Last night, Chancellor Alistair Darling dismissed his crackdown on parliamentary perks, saying: “Putting up the price of beer in the House of Commons does not add up to an economic policy.”

The Tory leader’s “age of austerity” measures came as the election battle lines were drawn more clearly on the key issue of public spending cuts.

Mr Cameron said: “You need to start the process of bringing spending down now,” insisting the UK Government’s planned £30bn spending increase next year was “unaffordable”.

In a speech in Cardiff, Mr Darling shifted Labour policy by emphasising how the UK Government would not flinch from “hard choices on public spending”, signalling cuts would have to come but only once the economic recovery was entrenched.

Thus, the forthcoming election is now being drawn in terms of Tory cuts in the short term versus Labour ones in the medium term; yet neither party has spelled out where they will fall.

As government and opposition set out their general economic approaches, the leading think-tank, the National Institute for Economic and Social Research, shone an optimistic light on the spending debate by claiming the UK economy was now out of recession, having grown in the three months to August by 0.2%.

“And in the restaurants on the parliamentary estate, you can treat yourself to a ‘lean salad of lemon and lime-marinated roasted tofu with baby spinach and rocket, home-roasted plum tomatoes and grilled ficelle crouton’ for just £1.70. That’s all thanks to you - taxpayers’ cash subsidising a politician’s food and drink,” he added.

Cameron: Vowed to cut number of Scottish MPs by 10%, if he wins General Election