The leaders of the three major parties will go head-to-head in the second live televised debate of the General Election campaign.
The debate in Bristol is expected to see Liberal Democrat leader Nick Clegg come under pressure from his two rivals, after his widely-praised performance in last week's broadcast gave his party a boost of up to 12 points in the polls, transforming the election into a real three-horse race.
Labour's Gordon Brown and Conservative leader David Cameron will seek to highlight Lib Dem policies on the Trident nuclear deterrent and the European Union, which they believe will prove unattractive to voters.
But in a 90-minute debate on Sky News focused on foreign affairs, Mr Clegg is likely to respond by reminding voters that his party opposed the Iraq War, which both Tories and Labour supported.
Domestic affairs and the economy are also certain to feature among the questions from the studio audience, on a day when crucial borrowing figures will indicate whether the Government is on track to meet its Budget forecasts.
Polls suggest that the "Clegg bounce" was still having an impact a week after last Thursday's debate, with Lib Dems continuing to pip Labour for second place. A ComRes survey for ITV and The Independent put Conservatives ahead on 35% to the Lib Dems' 27% and Labour's 25%, while a YouGov poll for The Sun had the Tories on 33%, Lib Dems 31% and Labour 27%.
There were signs of Tory-supporting newspapers putting the Lib Dem leader under intense scrutiny ahead of the debate.
The Daily Telegraph reported that regular payments from three Lib Dem donors were paid directly into Mr Clegg's private bank account before he became leader. A party spokesman said that the gifts went towards funding staff for his parliamentary office and were "properly made and declared".
Mr Cameron insisted he was "aiming for outright victory", but left open the door for co-operation with the Liberal Democrats if they held the balance of power.
"We are trying to win the election, we are trying to win outright," he said. "If it falls short of that we have to behave responsibly, make sure that we have a working government of this country and things get done."