The stakes could not be higher for Gordon Brown, David Cameron and Nick Clegg as they prepare for the second televised debate of the General Election campaign.

The response to last week's broadcast - the first of its kind in UK electoral history - left no doubt that the live debates have the power to shift opinion on an unprecedented scale.

Mr Clegg's widely-praised performance has electrified the election contest, sending his party soaring to undreamed-of heights in the polls and eliminating a commanding Conservative lead which had lasted almost three years.

Now the Liberal Democrat leader can expect to be subjected to more intense scrutiny than ever before, as his Labour and Conservative rivals seek to halt the bandwagon which has sparked talk of "Cleggmania".

Both Mr Brown and Mr Cameron have played down suggestions that they will take the gloves off in the second 90-minute debate in a bid to tear apart Mr Clegg's claim to be ready to take office.

The debate will focus on foreign affairs, giving Mr Cameron and Mr Brown the chance to target the Liberal Democrats over Europe, where their enthusiasm for greater integration and the euro is at odds with the scepticism expressed by voters in most opinion polls.

But the foreign affairs theme will also allow the Lib Dem leader to highlight his party's opposition to the unpopular war in Iraq, which was supported by both of his rivals.