The Tories and their EU allies

But others warn that the party will lose influence in Europe if it deserts the EPP, and breaks up the parliament's largest political group, the European People's Party-European Democrats (EPP-ED).

Here Conservative MPs Robert Goodwill and David Curry, both former MEPs, argue for and against the move.

"David Cameron must stick to his pledge to withdraw from the European People's Party and to found a new group opposed to the federalist agenda and committed to an open, free-market Europe.

He must resist tired and threadbare claims that the Conservatives will lose influence in Europe if they leave the EPP.

The EPP-ED has supported the Working Time Directive, the EU Constitution, the euro and an EU seat in the UN - this does not reflect British desires, principles or beliefs

The European People's Party and European Democrats (EPP-ED) is comprised of the federalist EPP and the more Eurosceptic British and Czech European Democrats (the ED).

The EPP maintains budgetary control over the entire group, and its federalist members dominate the agenda. The EPP-ED has supported the Working Time Directive, the EU Constitution, the euro and an EU seat in the UN. This does not reflect British desires, principles or beliefs, let alone those of Conservatives.

Some MEPs from the old guard claim that the EPP carries weight in the assignment of high-profile parliamentary jobs, but they are pulling the wool over our eyes. A new group of 50 or so members would still qualify to have a vice-president of the parliament and chairmanship of a committee like agriculture or fisheries.

Also, while committee chairmen have some influence, this may not be the most effective way to represent British interests. The EPP hasn't helped Conservatives get their voices heard. During the British EU Presidency, Tony Blair addressed the parliament on three occasions, but on two of them no British EPP member had a chance to speak.

Mr Cameron's leadership of the party has been marked by his readiness to embrace change. Nowhere is that more true and necessary than in his attitude towards the EPP and his quest to make common cause with parties who share his 'New Europe' vision."

"The Conservatives have complete freedom of action within the group which they exercise on vital issues like the constitution. The freedom they have inside the federation is as great as they would have outside it.

Business wants less regulation and better regulation - does anyone seriously think that we would get this better from leading an unstable fringe group?

In any case, Angela Merkel, German Chancellor and Christian Democrat leader, is the German leader whose attitudes most reflect Britain's since the war. She speaks of de-regulation and even returning powers to national states. She is emerging as the dominant European politician and interlocutor of the US. Berlusconi has gone; the French are in melt-down; Blair is on the way out. What a curious moment to cut ties with the Christian Democrat family.

Leaving the EPP-ED federation would damage British interests. Business wants less regulation and better regulation. Does anyone seriously think that we would get this better from leading an unstable fringe group rather than being one of the biggest elements of the biggest group in the parliament?

Of course the Christian Democrats have traditionally pursued a "federalist" agenda. But, quite frankly, this doesn't matter a row of beans. The European Parliament cannot bring into existence a European police, army, or tax system. What it exists to do is to scrutinise EU legislation which affects all our daily lives and the Conservative influence in this nitty-gritty business is much better served by being at the heart of decision-making not on the fringe."