Nick Clegg stakes his future on trial-by-debate with Ukip leader Nigel Farage

EU gamble could save Lib Dem seats or spark leadership race if it backfires

Nick Clegg will take part in the first of two debates with Nigel Farage on Wednesday night, with the second clash set for a week later (PA)

Nick Clegg’s high-risk strategy of advertising his pro-European credentials will be put to the test when he goes head-to-head with Nigel Farage in the first of two broadcast debates.

The Liberal Democrat leader is gambling that his appeal to the estimated 25 per cent of the public who are strongly committed to Britain’s EU membership will prevent his party suffering a meltdown in the European Parliament elections on 22 May.

The Lib Dems fear their group of 12 MEPs could be cut to two or even none. If that happens, Mr Clegg’s decision to break with tradition and talk about Europe in a Euro election will be seen as a disastrous mistake that raises big questions about his judgment.

It is a calculated risk: 25 per cent is higher than the Lib Dems’ 10 per cent rating in the opinion polls. “We are not asking people to vote for us at the general election; this is about Britain’s place in Europe,” said one Lib Dem source.

The Deputy Prime Minister decided to brand the Lib Dems as the “party of in”, a deliberate contrast with the UK Independence Party.

Although Mr Clegg was the unexpected star of the leaders’ televised debates at the 2010 general election, his aides insist he is “the underdog” against Mr Farage because public opinion is overwhelmingly hostile to the EU.

The leaders of the two smallest of Britain’s four main parties will lock horns in a one-hour debate hosted by the LBC 97.3 radio station at 7pm on Wednesday night, which will also be shown on Sky News. Their second clash, a week later, will be screened on BBC2.

The Conservatives and Labour dismiss the two debates as the “battle of the lightweights”. But they will be glued to them and will wonder whether they should have taken a seat at the table. Both the Lib Dems and Ukip will label the two biggest parties “too scared” to discuss Europe, claiming that Labour does not want to look pro-European to a Eurosceptic electorate and saying that the Tories are split on the whole “in-out” question.

Despite their very different visions of Europe, there is mutual respect between the Lib Dems and Ukip because of their willingness to engage on the Europe issue. Fittingly, as Mr Farage is normally photographed drinking beer, the terms of the two debates were settled amicably and speedily over a pint in The Iron Duke pub near Ukip’s Mayfair HQ, by Clegg aides Jonny Oates and James McGrory and Mr Farage’s communications advisers Patrick O’Flynn and Alexandra Phillips.

Mr Farage has been mugging up on his statistics and is keen to demolish claims that 3.5 million British jobs depend on EU membership. But there has been no dress rehearsal with someone acting the part of Mr Clegg. Mr Farage, who likes to think on his feet, told aides: “I do not want to be over-prepared.”

The Deputy Prime Minister’s team stresses that his “busy day job” has limited his time for war-gaming and arguing with a stand-in Mr Farage, adding that he is concentrating on “facts and figures” ahead of the debate.

Both parties sense a big opportunity, even though only one can emerge a winner. For Ukip, the debates mark another leg of its long march from single-issue pressure group to a threat to all three main national parties.

“Nigel has waited 20 years for this,” one Ukip aide said. “This is a big moment for us.”