British prime minister Gordon Brown is to subject himself to a grilling by Jeremy Paxman before the general election, his spokesman has said.

Lib Dem leader Nick Clegg's interview with the Newsnight presenter was aired last week. Brown will take part in a similar Panorama special on 26 April.

His Conservative counterpart, David Cameron, has yet to accept an invitation to take part in the series, although the Tories say negotiations continue.

A spokesman for Brown said: "Gordon has always said he's happy to answer any questions. He will be relishing the opportunity to debate the big choices facing the country."

Business secretary Peter Mandelson suggested Cameron was not keen to undergo a cross-examination by Paxman.

"David Cameron has so far refused to do the Paxman interview. We now know why. He doesn't like scrutiny and he doesn't like tough questions. The contrast with Gordon, who has agreed to do the Paxman interview, is obvious."

The interview with Cameron had been planned for this coming Monday but the Conservatives have asked the BBC for alternative dates.

A Conservative Party spokesman said: "We continue to talk to Panorama about the possibility of an inter- view."

Brown told supporters yesterday that the general election is "wide open" in the wake of the televised leaders' debate.

In a stump speech to party activists in Bedford, the prime minister said it was time to take the fight to Conservatives in key seats across the country.

He also said that, while the Lib Dems have gained an advantage from the TV debate, their policies will "unravel" as they and the Tories come under increasing scrutiny and pressure.

He said Labour should seek to exploit what it perceives as growing doubts about David Cameron's leadership fuelled by the ITV debate.

Meanwhile, foreign secretary David Miliband and defence secretary Bob Ainsworth launched Labour's defence and security manifesto, featuring further details on their commitment to the armed forces charter. They met veterans in south London.

European capitals are surveying the British election campaign with increasing anxiety. There is no recent precedent for a party so virulently Eurosceptic, or europhobic, as David Cameron's 'New Tories' taking office in a large EU member state.

Eight paragraphs out of the 120-page manifesto represents the founding wisdom of 'Daveism' on Europe, which states that the EU should become a loose "association" of states. In the meantime, there should be more opt-outs and exceptions for Britain, including on criminal justice and the charter of fundamental rights. There will be a law to ensure a referendum on any future transfer of powers to the EU. A Tory Britain will never join the euro.

On the surface, there is nothing especially revolutionary in all of that. No Ukip-like threat to leave the EU; no attempt to repeal the Lisbon treaty. All the same, continental governments are worried. According to a survey by the ConservativeHome website, more than 40% of Tory candidates favour outright withdrawal or a "fundamental renegotiation" of EU membership.

Alain Richard, a Socialist ex-French defence minister, said: "For many months there has been a tendency to say 'Oh, Cameron is British. He is pragmatic. There will be no real problem. Anyway, he may never be elected'. That mood is now changing, in Paris, Berlin and elsewhere, with a growing realisation that a Cameron government could be a serious threat to the stability of the EU, with potentially dangerous consequences at a time of recession. The mood now, even for centre-right governments like in Paris and Berlin, is 'Let's hope Cameron is not elected'."

Angela Merkel of Germany is hardly a euro-visionary, but she remains icily furious at Cameron's decision last year to abandon the mainstream, vaguely federalist, centre-right movement, the European People's Party, in favour of a ragbag of small eastern European nationalist parties.

"Under Cameron, the UK would be in danger of becoming an irrelevance in Europe," said one source in Merkel's Christian Democratic Party.

The same message – "You need us more than we need you" – was communicated to Cameron by the secretary general of the jilted EPP.

"[The Tories] have no influence and they have nothing to say within the EU institutions now," said Antonio Lopez-Isturiz, a Spanish MEP. "Being left out of the main political institutions in the EU is a mistake. I believe Cameron will make the pragmatic choice after the elections to come back."

There has been a relative Tory reluctance to discuss Europe during the campaign. A senior official in Brussels predicts a kind of "phoney war" if the Conservatives are elected on 6 May.

"My guess is that not much will happen initially with the Tories. They will keep a low profile on Europe. I think Merkel and [Nicolas] Sarkozy will try to embrace them in the large centre-right family again. But we'll have to see."

This could be the best of times or the worst of times for a Tory-led Britain to wrestle with its partners in the EU. Far from the federalist conspiracy of Ukip nightmares, the EU is drifting and leaderless. The ratification of the Lisbon treaty has not produced the stronger leadership, or "increased visibility", or sense of popular purpose, promised during eight years of negotiations. To some voices in France, for instance, the real threats to EU unity in 2010 are not Cameron and Britain but Merkel and a newly self-confident, and even selfish, Germany.

The EU, enlarged and semi-reformed, has already moved much closer to what moderate Tories say they want: a community of states founded on a single, free market and a desire to defend Europe-wide common interests on issues such as the environment. Talk of moving to an "association" of states – viz the Tory manifesto – is unhelpful, say mainstream continental politicians. Britain lost that argument in the 1950s.

The EU is founded on the twin principles of shared sovereignty and common legislation, where desirable. Without them, the single market, which Tories profess to support, could never have existed and would not survive. But enlargement to 27 states, with more to come, and the decline of the federalist religion in Germany and the Netherlands have changed many things. A subtle Tory government would have an opportunity to deflect a rudderless EU towards some of Britain's long-stated goals: more free trade in services; even less spending on agriculture; further enlargement.

"The problem is that this is not an argument you can easily make with the modern Conservatives," said one senior member of Sarkozy's party. "We find that we can no longer speak the same language as them on Europe... Cameron seems to me to have made a devil's pact with his backbenchers and the British press. He can abandon the whole of Thatcherism so long as he is more Thatcher than Thatcher on Europe."

A Cameron government would find itself confronted by the conundrum that has tormented British governments for 60 years. Left to itself, Britain would never have invented a sovereignty-sharing, law-making European Union. Once the EU exists, the game changes. Can Britain afford to flounce away from the whole project?