David Cameron is facing a confrontation with Angela Merkel, German chancellor, as rebel MEPs from his Conservative party prepare to defy his orders and vote for a pact with the anti-euro Alternative für Deutschland party.
The UK prime minister told Tory MEPs last week that they should not join forces with the AfD in a eurosceptic bloc in the European parliament, knowing such a move would be seen as hostile by Ms Merkel.
But a number of them have backed the admission of seven MEPs from the German party into the European Conservatives and Reformists group, which was founded by Mr Cameron in 2009.
If the group decides this week to embrace the AfD, seen by Ms Merkel as a rival to her own CDU/CSU party alliance, it would strain relations between Berlin and London at a critical time.
Mr Cameron is relying on Ms Merkel to help him secure reforms to the EU – including measures to reduce so-called “benefit tourism” by migrant workers and protection of British interests in the single market – ahead of his proposed in-out referendum in 2017.
He is also pressing the German chancellor to block the appointment of Jean-Claude Juncker, the federalist former prime minister of Luxembourg, as the next president of the European Commission.
“The prime minister’s position remains unchanged,” said a Conservative party official. “We have a sister party in the German CDU/CSU and we are not looking for another.”
But five Conservative MEPs have already signalled they will defy Mr Cameron. “Delighted that AfD, Germany’s moderate anti-euro party, wants to join the ECR group – look forward to voting for their membership,” said Nirj Deva, a Tory MEP, on Twitter.
Julie Girling, another Tory member, said that because Ms Merkel is backing Mr Juncker “there is now no reason not to admit the AfD to the ECR next week”.
Bernd Lucke, the AfD leader, already claims the support of Polish and Czech ECR members. Even without the likely rebellion, the 19 British Tory MEPs make up less than half the 46-strong ECR group, meaning the UK delegation can be outvoted.
Mr Cameron is opposed to Mr Juncker as commission president because he feels he represents an old-style Brussels elite, unwilling to contemplate radical reform or to hand powers back to member states.
Ms Merkel initially suggested she wanted to consider a wide range of candidates for the top job in Brussels. But last weekend she declared she would support Mr Juncker as the “lead candidate” of the centre-right European People’s party, which won the most seats in last month’s European elections.
“I now lead all the discussions precisely in the spirit that Jean-Claude Juncker should be president of the European Commission,” she said.
Mr Cameron’s fight to stop Mr Juncker has intensified over the past few days – he has been lobbying the leaders of Finland, Sweden, Hungary, the Netherlands and Ireland to join him in arguing for a wider field of candidates.
Elmar Brok, a senior CDU MEP, said there was “no doubt” there would be negative consequences if the Tories aligned with a rival of Ms Merkel’s party. He said AfD was “far to the right and anti-euro”.
Meanwhile, one of Angela Merkel’s closest allies in the Christian Democrat party urged Mr Cameron to make clear the benefits of EU membership.
Gunther Krichbaum, chair of the Bundestag’s European affairs committee, said: “We ourselves as the CDU distinguish ourselves clearly from the AfD. From our point of view it is a rightwing populist party, and we have absolutely nothing in common.”
Ulrike Guérot, senior associate for Germany at the Open Society Initiative for Europe, said the AfD might hope to gain credibility in the next Bundestag election from an alliance with the Tories.
“Their target is to be in the Bundestag in 2017. To do this they need to shape the discourse to say that they are a national Conservative party. “If [Bernd] Lucke could be in a group with the Tories, he could make the point that he isn’t a populist.”
Mr Cameron will this week attend a G7 summit in Brussels, which includes a bilateral meeting with US President Barack Obama, followed by a head-to-head meeting with Vladimir Putin on the margins of events to mark the 70th anniversary of D-day.
Mr Cameron’s team say he will press the Russian president to seize the opportunity given by Ukraine’s elections to ease tensions in the region.
David Cameron and Angela Merkel
David Cameron needs support from the German chancellor to deliver his promised EU reforms ahead of a 2017 election. But Ms Merkel will be furious if Tory MEPs form an alliance with the Alternative für Deutschland, an anti-euro rival party to her own CDU/CSU alliance.
David Cameron and Jean-Claude Junker
Mr Cameron is keen to stop the former Luxembourg prime minister becoming European Commission president. Mr Juncker, a supporter of EU integration and the lead candidate of the centre-right European People’s Party, says his group won last month’s European elections and the job should be his.
David Cameron and Andrew Lansley
Mr Cameron is lining up Andrew Lansley, his long-term political ally (and former boss at Tory central office) to be Britain’s next European commissioner. But some rightwing Tory MPs say Mr Lansley, architect of the government’s health reforms, is not up to the job of taming the Brussels bureaucracy.