Anti-European Union protest parties could win as much as 31 per cent of the vote in the elections to the European Parliament next month, taking 218 out of 751 seats, a gain of 54 seats.

However the effect of this would be, ironically, to create a parliament even more in favour of greater centralised powers for the European Union. This is because the protest parties will crowd out the reformist parties, such as Britain’s Conservatives, and would mean trouble for David Cameron’s attempts at EU reform.

In effect the parliament will be polarised with a fragmented minority anti-EU bloc facing an overwhelming-majority integrationist bloc made up of centre-right and centre-left parties which all either support the status quo in Brussels, or want the EU to take on even more powers.

According to a briefing paper out today from the Open Europe think tank, this election result could spell trouble for Cameron’s plans to attempt to reform the EU: “The European Parliament will have an effective veto over some of the key items on his EU reform agenda, such as EU-US free trade talks and reforming EU migrants’ access to welfare.”

The vote-share of parties identified by Open Europe as being “critical reformers” – parties which believe the EU needs fundamental reform if it is to survive – is set to drop from 53 to 39 seats.

“Critically, we project that the share of MEPs explicitly dedicated to free market policies could also fall – from 242 (31.6%) to 206 (27.4%).”

Free-trade MEPs will likely decrease in number in May’s elections

Open Europe sees a “Commission-hugging European Parliament” and says “opting for even more centralisation will only further fuel the anti-EU vote.”

“If the turnout is roughly the same this time around (43%), we estimate that 74.4% of all voters will have voted against the EU, for radical change, or not bothered to vote at all, with only 25.6% of all eligible voters actively voting in favour of status quo/more integrationist parties.”

“For the European Parliament to pursue an explicitly integrationist agenda on such a thin public mandate would not be democratically honest – and would most likely serve to fuel the anti-EU vote even further.”