Conservative group to decide on Merkel adversaries

But if the party of British PM David Cameron accepts the alliance with Merkel's adversaries, this would be seen as a snub at a time when the two leaders disagree on who should run the EU commission.

The AfD was founded last year and is challenging one of Merkel's dictums - that there is no alternative to the euro.

They have called for the break-up of the eurozone or at least the temporary exit of weaker euro states and feel as strongly about 'welfare tourism' as the Tories do.

EP sources told EUobserver it is likely the Tories will vote against the AfD, but will still be "outvoted" by other ECR members. Of the 55-strong group, only 20 are Tories.

This would allow Cameron to tell Merkel his people did not agree to the German deputies joining, but were unable to prevent it.

"Merkel will not like this. They have gone behind her back from the very beginning and of course she will see through it," one EP source told this website.

Another source downplayed the impact this will have on German-British relations, pointing to Merkel's good personal ties with Cameron and that the AfD is likely to become more established in Germany, possibly even join a government with Merkel's Christian Democrats one day.

The ECR's success comes although the Tories were outvoted by the eurosceptic UK Independence Party in the May EU elections and their former group leader, Martin Callanan, lost his seat.

But while Ukip is having trouble forming a coalition in the EP (needing 25 deputies from seven member states), Cameron's Conservatives are having better luck. Both the eurosceptic Danish People's Party and their Finnish counterparts left Ukip to join the ECR group.

The faction may also get a boost from four Flemish separatist (N-VA) MEPs, who are deliberating whether to join ECR or the Liberals.

Italy's newly elected Five Star Movement of comedian-turned-politician Beppe Grillo also has 17 MEPs to offer. In an online referendum starting Thursday, the members of the party will choose which group to join - the ECR is one of the three options.

First Muslim leader?

The ECR on Thursday is also set to elect its new leader, with Syed Kamall tipped as favourite.

The 46-year old MEP from London, who led the British delegation since 2013, would be the group's first Muslim chairman.

He is of Guyanese descent after his father migrated from South American country in the 1950s and earned his living as a bus driver in London.

The other candidate for the ECR leadership is Charles Tannock, also from London. The 59-year old started off as a psychiatrist and was an MEP for the past 15 years.

In a sign of their ambition to become king-maker if they outnumber the Liberals by 24 June - the cut-off date for EP groups to be formed - the ECR has already put forward a candidate for the presidency of the European Parliament: Sajjad Karim, who was the first British Muslim to be elected to the EP in 2004.