Alistair Darling is expected to announce a higher rate of income tax for top earners as he sets out how he will claw back a multi-billion boost to the shrinking economy.
The Chancellor was said to be unveiling the plan for a 45% top rate on people earning at least £150,000 a year in his Pre-Budget Report
But the new tax band would not be introduced until after the next general election, which must be called by May 2010 at the latest.
It is thought to be among a series of deferred tax increases designed to bring down borrowing incurred now to fight the recession.
The PBR is expected to see Value Added Tax cut from 17.5% to 15% as part of a £15 to £20 billion "fiscal stimulus" to encourage spending and spur economic growth.
The plans will send borrowing soaring above £100bn, leading to Conservative accusations that Labour is storing up a "tax bombshell" in a reprise of the Tories' 1992 election campaign.
The Treasury refused to comment on the apparent leak of the 45% tax rate to several newspapers, describing it as "speculation".
But ministers repeatedly stressed that Mr Darling would set out in the PBR how he intended to get the public finances on a more stable footing later on."
Conservative leader David Cameron warned that the plans will send borrowing soaring above £100 billion next year, forcing sharp tax rises in the future.
Read More
In a speech to the CBI national conference, Mr Cameron said: "They might be talking about tax giveaways but everyone knows that they're throwing money at us now to take it away at a later date. To pay back all this money would mean an 8% rise in income tax, or a 6% rise in VAT, or a corporation tax rate of 71%."
