Ukip's deputy chairman Suzanne Evans has joined Douglas Carswell in openly defying the Eurosceptic party's ruling body by continuing to back the Vote Leave campaign. Evans told IBTimes UK that she would carry on supporting the group despite the National Executive Committee's (NEC) decision to back a rival Brexit campaign.

The organisation, along with Ukip's MEPs and Local Councillors Association, threw its support behind the Grassroots Out (GO) group. "We have been hoping and working for a rapprochement between the two main contenders for the designation, Vote Leave and Leave.EU. Unfortunately that has proved elusive," said Ukip chairman Steve Crowther.

"Meanwhile, GO has emerged as the genuinely cross-party, well-organised, energetic campaigning group, which has the momentum and is drawing in support from all quarters. We felt it was time to make a decision and get out on the campaign trail."

The GO campaign, founded by Labour MP Kate Hoey and two Conservative MPs, Peter Bone and Tom Pursglove, initially said it would not compete for the Electoral Commission's official Brexit campaign designation.

But now Leave.EU, which was co-founded by Ukip donor and GO backer Arron Banks, has also announced its support for the group. Meanwhile, the decision from Ukip's NEC means that any of its members could breach the party's rules by supporting Vote Leave.

However, like Evans, Carswell is staying put. "I'm 100% on board with Vote Leave and I'm more confident than ever that Vote Leave will get designation," the Clacton MP told The Spectator. The magazine also claimed that party figures are "unhappy" with the NEC's ruling since the body apparently did not meet in person.

A spokesman for Vote Leave, which recently reshuffled its top brass amid claims of in-fighting, said: "We wish Arron Bank's GO campaign well."

David Cameron has not yet set a date for the EU referendum as he continues his renegotiation with Brussels. But the prime minister is expected to pick 23 June for the historic ballot. The Electoral Commission will begin its Brexit campaign designation process once the Conservative leader has selected a date.

The latest opinion poll from YouGov for The Times, of more than 1,600 people between 3 and 4 February, put the leave vote nine points ahead of remain, at 45% versus 36% respectively.