THE anti-EU group supported by Tory heavyweights Boris Johnson and Michael Gove has been designated the lead Brexit campaign in the EU referendum amid confusion over a possible legal challenge by a rival camp.

The Electoral Commission - the official elections watchdog - said it had selected the Vote Leave campaign as it had "well-developed plans and structures" to work with other pro-Brexit groups in the run up to the vote on June 23.

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THE anti-EU group supported by Tory heavyweights Boris Johnson and Michael Gove has been designated the lead Brexit campaign in the EU referendum amid confusion over a possible legal challenge by a rival camp.

Leave.EU - the group founded by wealthy Ukip backer Arron Banks, which was supporting the application by the rival Grassroots Out (GO) campaign - swiftly announced it would seek a judicial review.

After consulting lawyers, Mr Banks warned that the move could force the UK Government to put back the date of the referendum to October

"I am thoroughly unsatisfied with the Electoral Commission's decision for a variety of reasons that I will be making clear in my application for judicial review," he said.

However, in a terse one-sentence statement issued just 40 minutes later, Leave.EU said it would make a decision on whether to proceed with a judicial review by midday on Thursday. There was no explanation for the apparent change in position.

The reaction of Mr Banks and Leave.EU was in sharp contrast to GO co-founder, Tory MP Peter Bone, who immediately offered to help build a "united front" to secure a vote for Brexit.

"We look forward to working closely and productively with all those who want to see the UK set free to determine its own destiny," he said.

Ukip leader Nigel Farage, who was also backing GO, likewise looked to build bridges saying his party would work with anyone who wanted to leave the EU.

"I have always wanted all on the Leave side to come together and have done my best to try and make this happen. I'll continue to do so in the run up to the referendum to ensure the Leave side wins," he said.

The commission's decision was criticised by the left wing Trade Unionist and Socialist Coalition (TUSC) which lodged a surprise 11th hour bid for the Leave designation.

TUSC chair Dave Nellist said: "It is not a surprise to us that the Electoral Commission has bowed to political pressure and chosen the opponents that the establishment want to fight and not the ones who could have given them a proper contest."

A spokesman for Vote Leave said: "We will continue to work constructively with everyone who wants to campaign for a Leave vote."

As expected, the commission named the only contender on the In side - Britain Stronger In Europe, fronted by former Marks and Spencer boss Lord Rose - as the designated Remain campaign.

Electoral Commission chief executive Claire Bassett said they had two "high quality applications" on the Leave side from Vote Leave Ltd and The Go Movement Ltd representing GO.

"After careful consideration, the commission decided that Vote Leave Ltd better demonstrated that it has the structures in place to ensure the views of other campaigners are represented in the delivery of its campaign," she said.

"It therefore represents, to a greater extent than Go Movement Ltd, those campaigning for the Leave outcome, which is the test we must apply. We encourage all campaigners to now focus on engaging voters on the historic decision they will have to take on June 23."

The decision gives Vote Leave permission to spend up to £7 million on the coming contest, compared to just £700,000 for other registered campaign groups on the Leave side, as well as access to a grant of up to £600,000, free mail-shots and guaranteed TV broadcasts.