Europe's leaders were plunged into a power struggle over who gets the biggest job in the EU late on Tuesday, with David Cameron seeking to drum up support to prevent a veteran insider becoming the new head of the European commission. He won cautious and qualified support from the key player, the German chancellor, Angela Merkel.

As national heads of government held a Brussels summit to consider their options after a tumultuous European election that was tantamount to a vote of no confidence in many of the leaders, Cameron attacked the EU as being "too big, too bossy, too interfering".

The fallout from the weekend elections began to hit politics across the continent when a senior member of the German government labelled France's Front National (FN) "fascist", a description that was echoed by a senior member of the commission, following the FN's rout of the mainstream parties in the ballot in France.

Europe's Christian Democrats emerged as the biggest caucus in the new parliament and the main parliamentary leaders on Tuesday claimed that as a mandate for their contender, Jean-Claude Juncker, the former prime minister of Luxembourg, to be nominated as next head of the commission, a choice vehemently opposed by Cameron.

The parliamentary leaders demanded that the summit rubber stamp that nomination. Cameron was joined by the Hungarian and Swedish prime ministers in rejecting Juncker.

"Europe cannot shrug off theses results. We need an approach that recognises that Europe should concentrate on what matters, on growth and jobs and not try and do so much," said Cameron.

"We need an approach that recognises that Brussels has got too big, too bossy, too interfering. We need more for nation states. It should be nation states wherever possible and Europe only where necessary. Of course we need people running these organisations that really understand that and can build a Europe that is about openness, competitiveness and flexibility, not about the past."

In the past 48 hours, Cameron has phoned several leaders, including Angela Merkel of Germany, in an attempt to build a "stop Juncker" coalition. Merkel hedged her bets while declaring that Juncker was her favoured candidate. But she also strongly rejected the ultimatum from the parliamentary leaders, warning of a "catastrophe" if the national governments bowed to the pressure.

She made clear that the leaders would not be rushed into any decisions demanded by the parliament, saying it would be the end of next month at the earliest before a proposal was made. While declaring her support for Juncker, she also signalled many reasons why he might not secure the post.

"Jean-Claude Juncker is our top candidate," she said. "But firstly it is about content. We know we can't manage this alone, but need a coalition."

Parliamentary leaders of five of the seven main voting blocs insisted that Juncker be charged with trying to cobble together a majority supporting him as president of the commission. But it is up to the national leaders, not the parliament, to propose a new commission president. Merkel emphasised that the decisions deciding a policy programme for the next five years and that too much was at stake. "Thoroughness, not speed" was the main thing, she said.

She also said that the leaders had to cooperate well over that period, signaling she did not want to isolate Cameron but would seek a consensus on who should get the job.

The parliament's move represented the first gambit in what promises to be an exhausting protracted battle between rival EU institutions over who gets to decide the next commission president.

The Hungarian prime minister, Viktor Orban, said Juncker could "definitely not" get the job. Cameron was also supported by the Swedish leader, Frederik Reinfeldt. But Cameron cannot veto the choice, which is carried by the majority.

Cameron and the French president, François Hollande, led their parties to historic defeats at the hands of the extreme right in Britain and France and appeared to be in a weak position at the summit following the disastrous outcome.

Recrimination and anxiety among the EU's elite surfaced particularly over developments in France.

Speaking at a conference in Berlin, Wolfgang Schäuble, the German finance minister and one of the most influential politicians in the EU, deplored the outcome of the European election in France where Marine Le Pen's FN made its biggest breakthrough to win the ballot with 25% of the vote.

"A quarter of the electorate voted not for a rightwing party but for a fascist, extremist party," said Schäuble.

It is not clear how the remarks will be received in France. Relations between Paris and Berlin have been frosty since Hollande was elected president two years ago, with much of the French elite bridling at the perceived hegemony of Berlin at the height of the euro crisis. Le Pen has previously gone to court in France seeking to ban her party being labelled "fascist". She lost.

Le Pen's current ascendancy contrasts with the dire state of the mainstream parties in France. The leader of the Gaullist centre-right UMP, Jean-François Copé, resigned on Tuesday due to sleaze allegations and the party appears to be in meltdown, while Hollande's governing socialists sank to 14% in the European election, their worst ever performance.

The attack on the FN was taken up by Viviane Reding, the vice-president of the European commission. Asked by a Swiss television station whether the FN's triumph imperilled democracy in Europe, she responded: "It is absolutely dangerous, like all fascism."

While neo-fascists from Greece, Hungary and Germany won seats in the Strasbourg parliament, the far right also scored dramatic victories in Britain and Denmark and did well in Austria.

On the other side of the political spectrum, the hard left also won the election in Greece, did well in Ireland and boosted its presence in several countries. Reding branded some of them as fascist, too. "There is also the fascism of the left which will be in the parliament."