Image copyright PA Image caption Mr Carswell said the EU referendum must be the party's main focus

Douglas Carswell has said UKIP must be willing to "work with anyone" to win the vote on the UK's future in Europe.

He told activists that the party must "radiate optimism" and its recent success would be "worthless" if the UK did not leave the European Union.

His message comes amid divisions over which anti-EU campaign group to back.

Party leader Nigel Farage has endorsed the umbrella Leave.eu group while Mr Carswell has suggested he would back a separate group, Business for Britain.

On Friday, Mr Farage suggested this difference of opinion showed Mr Carswell had "residual loyalties" to the Conservatives - from whom he defected last year.

In his main address to the party's conference in Doncaster, which came after a day of behind-the-scenes tensions between UKIP's sole MP and other UKIP figures, Mr Carswell said UKIP must throw everything it had at the in-out referendum on Europe, to be held before the end of 2017.

'Upbeat'

Mr Carswell urged the party to make an "upbeat" case for leaving the EU, arguing the UK was "more tolerant and open than ever" and UKIP "must never blame outsiders" for problems caused by politicians.

"We must be prepared to work with anyone, left or right, politician or undecided," he said. "There are good patriotic politicians in all parties and we must work with them all."

He thanked UKIP members for helping electing him twice in the space of eight months, firstly in a by-election and the general election, saying "my win in Clacton wasn't my victory, it was UKIP's victory, it was their victory".

He told the BBC he was "very loyal to people called Eurosceptics in all parties", insisting "we're on the same side" and he had no doubt about remaining in UKIP.

The gathering in Doncaster is being dominated by the forthcoming referendum on the UK's future in Europe, with Mr Farage urging activists to seize the opportunity of the first public vote on Europe for more than 40 years.

The exact date of the referendum has yet to be announced and the official "in" and "out" campaigns and who will lead them have yet to be officially announced.

Speaking to delegates on Friday, Mr Farage appealed to his members to put "country before party" over the next two years and hailed a "show of unity" among anti-EU groups, who have formed Leave.eu to push for a UK exit.

Several of the disparate groups now joining forces within Leave.eu addressed the conference.

Media playback is unsupported on your device Media caption Nigel Farage: "We want our country back"

But Mr Carswell has suggested Business for Britain is a better vehicle to lead the "Out" campaign despite its not being part of Leave.eu and having yet to categorically commit itself to backing EU exit pending the outcome of Prime Minister David Cameron's negotiations with EU leaders.

Mr Carswell says Business for Britain's founders, who have links to the Conservatives, are "individuals with a proven track record of winning referendums".

'Big chin'

The Clacton MP had an angry exchange of views on the matter with Arron Banks, a UKIP donor and leading light behind Leave.eu, at the conference.

It followed a claim in the Guardian that Mr Banks suggested Mr Carswell could face deselection from UKIP, if he endorsed a different eurosceptic campaign.

Mr Carswell dismissed comments made about him by Mr Banks that he was "borderline autistic" with mental illness, saying "politics can be a rough trade. I have a big chin and take it in my stride".

On the second day of their conference, UKIP have been making the case for reform to the UK voting system following May's election, in which it only won one seat despite getting nearly four million votes.

The party also announced that Peter Whittle will be its candidate for the 2016 London mayoral election while broadcaster Mike Read is among 11 candidates for the London Assembly.