The stakes could not be higher for British finance minister Alistair Darling when he delivers his pre-Budget report today - an election must take place within six months and his Labour Party is on course to lose.

Mr Darling looks set to announce tax rises that may do little to dent the record deficit but could make inroads in the opinion polls by cashing in on anger against the banks for causing the worst recession since World War II.

Under consideration is a tax on bankers' bonuses, according to government sources. One option is a levy on banks at a rate of something like 50 per cent who pay bonuses akin to employers' National Insurance contributions.

But the annual set-piece may turn out to be a non-event for financial markets beyond traders' worries about the impact on their wallets. Markets expect the opposition Conservative Party to be in power by June and know anything Labour announces now may never come to pass.

Conservative leader David Cameron rammed the point home yesterday, repeating his pledge to hold an emergency Budget within 50 days of taking office, if elected.

That is complicating life for analysts and policymakers trying to get a handle on just where the economy is headed. Few doubt that big tax rises and spending cuts are on the way but no political party is going to spell them out before an election.

Aside from targeting bankers, there could also be changes to the inheritance and capital tax regimes which would raise some money but also help portray Labour as the champion of hard-working families against a Conservative Party that panders to the rich.

Mr Cameron hit back at such accusations at the weekend, saying Prime Minister Gordon Brown's jibes about his privileged upbringing were petty and spiteful. But Labour looks likely to persist with this line of attack as it tries to narrow the Conservatives' poll lead.

With the Budget deficit already at a record high, markets are eager for every titbit on how any government plans to bring it down. Ratings agency Moody's Investors says the fiscal crisis in Britain and other top-rated countries could last for years.

Labour is clearly hoping a hardline on bankers' pay will be able to give it some momentum in the polls which despite some narrowing in their lead still mostly show the Conservatives on course for victory at an election expected next May.