Change UK has been formally registered as a political party, allowing the centrist movement founded by former Labour and Tory MPs to field candidates for the European elections.

The group, led by the former Conservative Heidi Allen, has received more than 3,700 expressions of interest in being a candidate in the elections and is polling about 4-7% for the contest, meaning it could get MEPs.

Change UK’s registration was accepted by the Electoral Commission but the body rejected its proposed emblem. A spokeswoman for the commission said: “The emblem contained a hashtag, and we cannot assess the material linked to a hashtag, which will change over time, against the legal tests. The emblem also contained the acronym TIG, which we were not satisfied was sufficiently well known.”

Allen said the party had been “overwhelmed by the thousands of people wanting to roll up their sleeves and join our campaign from every walk of life and every corner of the country”.

She added: “Change UK – the Independent Group – have a clear message in the European elections: we demand a people’s vote and, if it is held, all our MPs will campaign to remain in and reform the European Union.”

The party will announce its MEP candidates at a launch event next week and has set up a European elections fighting fund to solicit donations.

The polls are likely to bring some success for both the pro-referendum Change UK and the new Brexit party led by Nigel Farage, as voters punish the Conservatives for the paralysis over leaving the EU.

The Brexit party is polling in double digits at about 12%, while Ukip, which has moved to the far right and become an anti-Islam party under Gerard Batten, is on about 13%, according to the latest Opinium survey.

This suggests in combination they could do better than the Conservatives, who have dropped below 20%.

Farage, who left Ukip to found his own pro-Brexit party, claimed his party would “sweep the board in these elections unless [Theresa] May and Jeremy Corbyn reach a deal involving a customs union before then”.

He added: “If that happens, the Brexit party won’t win the European elections, but it will win the general election because the betrayal will be so complete and utter, so I don’t believe it’s going to happen.”

In contrast with the newly established parties, the Conservative activist base is extremely demotivated, with members unwilling to campaign in elections that May had promised would not take place because Brexit was meant to have happened on 29 March. Some pro-Brexit Tories are also unhappy the pro-EU MEPs Charles Tannock and Sajjad Karim are standing again on the list.

Labour is not expected to perform badly in the European elections, but has a dilemma over whether to promise a second referendum in its manifesto for the contest or stick to its line that it is an option on the table to stop a damaging Tory-led Brexit.