Calculating: Brown will plunge the UK into debt to win over voters

Gordon Brown was accused of 'gross fiscal irresponsibility' last night as it emerged Britain's budget deficit could double to a staggering £60billion.

Dismal growth estimates from the Bank of England suggest the black hole in this year's public finances is set to be the largest since post-war records began.

Shadow Chancellor George Osborne will today claim the Prime Minister is preparing to try to 'buy his way out of trouble by bribing people with their own borrowed money'.

He will accuse Mr Brown of pursuing policies that are 'deeply unfair' on future generations who will have to pay the debts he is building up.

Labour, he will say, is a party 'willing to mortgage the country for its own short-term survival'.

In a major speech to the centre-Left think-tank Demos, the Shadow Chancellor will also seek to draw a comparison between Mr Brown's expected autumn relaunch - based on the theme of 'fairness' - with the one attempted by the Tories' ill-fated ex-leader Iain Duncan Smith.

'I remember an attempted Conservative relaunch in 2003 was based on the theme of 'A Fair Deal for Everyone', ' he will say.

'It was not a great success - indeed we lost our party leader that autumn. And I suspect Gordon Brown's relaunch too will fairly and squarely fail. Why?

'Because it is nothing other than a political rescue plan, not a coherent organising principle.'

Mr Osborne will suggest that the Tories would introduce an independent mechanism to prevent any government borrowing irresponsibly.

And in an audacious raid on Labour's traditional territory, Mr Osborne will also mock Labour for adopting the 'fairness' theme and claim only the Conservatives can deliver a truly fair society.

'I've seen the focus groups too. People like the word 'fair',' he will say. 'They think government is 'unfair' to those who work hard and play by the rules. They want a 'fair deal' and 'fair play'.

Fears: Shadow Chancellor George Osborne is worried Brown's spending spree will leave a messy legacy for the Tories

'When you're in trouble as a political party, there is a temptation to cling desperately to the words focus groups throw up.'

But Mr Osborne will claim Mr Brown's belief that only the state can deliver fairness is doomed to fail.

He will say that a fair society is one where people are rewarded for their efforts and abilities, and where they can achieve their aspirations regardless of their background.

His speech will be seen as an attempt to spike Labour's guns ahead of an 'economic recovery plan', which is expected to include measures to ease the burden of rising food and energy prices, including fuel vouchers for the poor and a possible stamp duty 'holiday'.

Even senior Treasury officials admit there is no money to spare for expensive measures.

The Government has already borrowed an extra £2.7billion to try to offset the impact of the scrapping of the 10p tax rate.

The latest growth estimates, which suggest the gap between tax receipts and public spending is set to widen dramatically, will add to pressure on Mr Brown to explain how he intends to pay for any further measures.

They will also raise fears that tax increases will be needed to restore the public finances to health.

An update from the Bank of England last week revealed it expects economic growth to be almost zero early next year.

This compares with optimistic growth forecasts of 1.75 per cent released by the Treasury in March.

If the economy flatlines, this could widen the hole in its books to £59billion in the current year and £60billion next year.

That would mark a doubling in the deficit in just two years and is significantly worse than the £43billion deficit the Government is currently predicting.

The calculations are based on a formula used by the Institute for Fiscal Studies.

Labour's Exchequer Secretary Angela Eagle MP accused Mr Osborne last night of 'more shallow salesmanship'.

'George Osborne can have no credibility until he explains how he would reduce borrowing when the Tories have promised over £10billion of unfunded tax cuts and billions of pounds of spending promises,' she said.