The new Independent Group of 11 former Labour and Tory MPs will take the first steps towards becoming a fully fledged political party that can take on the Tories and Labour at the next general election, amid growing rumours that more defectors could soon join their ranks.

MPs from the group will open talks with the Electoral Commission on Tuesday to discuss what moves they must take to register as a party that can put up candidates nationwide if the current political turmoil over Brexit leads to a snap election.

Following the dramatic decision by eight Labour MPs and three Tories to split off from their parties less than a fortnight ago, the group believes it must be ready at the earliest opportunity to offer voters a new option on the centre ground of British politics.

The former Labour MP Chris Leslie said that the plans to form a party could not be delayed at a time when millions of voters were feeling increasingly disillusioned with the established parties.

“We can’t leave the British public with a choice between Corbynism and Europhobia at a general election – which means we have a duty to develop a serious alternative,” he said.

“It has been hard but necessary to leave behind the broken political parties, but now we must get on with the urgent task of creating something new that the majority in the mainstream of British public opinion can support.”

The commission requires a new party to provide information about its finances and constitution and to appoint people to the roles of party leader, treasurer and nominating officer.

A decision by the group last week to appoint former Labour MP Chuka Umunna as its overall spokesman was seen as a sign that he will, in all probability, take on the role of leader, perhaps with one of the three former Tories - Sarah Wollaston, Heidi Allen and Anna Soubry - as deputy.

Umunna made no secret of his desire to lead the group last week when he said in a TV interview that he hoped to play “the biggest role” in the breakaway group. The group is likely to stick with its current name.

It is understood that the group has received donations amounting to several hundreds of thousands of pounds from many hundreds of small donors, and is now actively seeking larger-scale financial backing that will allow it to fund central and regional offices and electoral campaigns.

Members of the group are planning a series of regional meetings around the country in the next few weeks at which they hope to attract disaffected supporters of the existing main parties.

Sources said that talks were under way with several other Labour MPs –and more Tories – who are unhappy and also considering defecting.

The difficulties the group will face in maintaining momentum and building a profile were underlined last week when an amendment it put down calling for another Brexit referendum was not called by the Commons Speaker, John Bercow.

The former Labour MP Luciana Berger, who quit Labour over its handling of antisemitism, was also not selected at prime minister’s questions by Bercow.

The Independent Group has yet to make any substantial breakthrough, according to a new Opinium poll for the Observer. When members of the public were asked who they would vote for if a general election were called tomorrow, just 5% picked the Independent Group.

The poll reveals that the Tories are on 37%, four points ahead of Labour on 33%. The Liberal Democrats and Ukip are both on 7%.