Chancellor Gordon Brown is preparing to deliver his 10th Budget to MPs in the House of Commons.
Mr Brown: Preparing for Number 10?
Giveaways are not expected in the annual statement, due at 1230GMT, outlining his tax and spending plans.
Reports suggest the private finance initiative may be expanded and "gas guzzling" 4x4 cars may face tax rises.
It will be his first big clash with the new Lib Dem and Tory leaders, who are expected to be his rivals at the next election if he succeeds Tony Blair.
The whole event will be closely watched for signs Mr Brown expects to have succeeded Mr Blair in No 10 by the time of next year's Budget.
Mr Brown told the Cabinet that increased economic competition from China and India meant the government could not "afford to be complacent or for there to be any relaxation of fiscal discipline".
The Budget would "make the most of the opportunities of globalisation", he added.
Conservative leader David Cameron will respond to Mr Brown's speech at about 1320 GMT, with Lib Dem leader Sir Menzies Campbell speaking from about 1345 GMT, although all timings are subject to change.
According to The Guardian newspaper, Mr Brown will unveil a £26bn expansion of the controversial Private Finance Initiative (PFI) across 200 public sector projects.
The proposals, which the paper says will be in background papers, will be the biggest expansion of PFI, which uses private money to build and run hospitals, schools and other services, in the world.
The Sun meanwhile reports Mr Brown will cap pay rises for judges, hospital consultants and top civil servants below inflation to allow bigger rises for soldiers, nurses and teachers.
Other measures tipped to be in this year's Budget include:
- A repeat of last year's £200 council tax rebate for pensioners
- Increasing council tax for households that throw away too much rubbish
- More help to get single parents into work
- More cash for military operations in Iraq and Afghanistan
Tory shadow chancellor George Osborne said he feared the Budget would suffer from Mr Brown's personal political ambitions.
He said: "Does Gordon Brown actually use this Budget to address the big challenges that Britain faces - pensions reform, environmental issues, our ability to compete against China and India - or does he make the mistake of trying to use this of a leadership bid because of the problems that Tony Blair has?
"I fear this is going to be long on all sorts of rhetoric about where a Brown premiership would take us rather than specific measures that would help our country compete in the future, help people listening to this programme pay their mortgage, get a good job, have decent public services."
Lib Dem Treasury spokesman Vince Cable said extra tax on "gas guzzlers" would be welcome but a "small step" in a much bigger picture.
"The overall story is that carbon emissions are rising now quite strongly from the UK and we are falling behind any expectations we had of meeting the Kyoto target," said Mr Cable.
"He should be addressing much bigger issues like the enormous growth of emissions in the aviation sector where there isn't a system of taxation or charging which reflects pollution."
You can watch live coverage of the Budget here on the BBC News Player or on BBC Two and BBC News 24 from 1130 GMT.