TIM Farron will accuse Jeremy Corbyn today of “throwing in the towel” in the fight to keep Britain in the European single market.

The attack in the Liberal Democrat leader’s speech on Europe will come as conference is expected to endorse his call for there to be a second referendum on the final Brexit deal – “with the option of the UK remaining in the EU”.

Mr Farron will say: "The Liberal Democrats demand that the British people should have their say on the final Brexit deal in a referendum. Voting for a departure is not the same as voting for a destination. The British people should be allowed to choose what comes next to ensure it is right for them, their families, their jobs and our country.”

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In the meantime, he will tell delegates, that his party will fight for the best deal possible, which means Britain remaining in the single market.

“Nothing is more important to Britain's economic future. Nothing will make more difference to British jobs and British businesses,” the Cumbrian MP will declare.

"Jeremy Corbyn has already thrown in the towel. He didn't make an effort to keep us in Europe during the referendum campaign and now he has made clear he won't fight for our membership of the single market.

"Under Jeremy Corbyn, Labour is simply not doing its job as the opposition and nowhere is that clearer than on Europe. So if he won't, we will.”

Mr Farron will add: "My message to pro-European Labour supporters is clear: Jeremy Corbyn is not on your side. The Liberal Democrats are the only party fighting to keep Britain in the single market. We are the real voice of opposition to the Conservative Brexit Government and the only party fighting to keep Britain open, tolerant and united."

At conference, Alistair Carmichael, the former Scottish secretary, described the June 23 referendum as “unsatisfactory,” because it was a contest between a known and an unknown.

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“When you get to having the actual terms of the deal nailed down, then you have a contest between two known propositions. At that point, the deal should be put to the people of Britain. I’m optimistic in that context you would have a different debate and the cause could still be won.”

The Lib Dem MP for Orkney and Shetland said this process was different from the 2014 Scottish independence referendum.

“The first EU referendum was on the principle; the permission to negotiate if you like. The Nationalists were denied that permission in 2014. What the SNP want to do is essentially what the Irish did with the Lisbon Treaty: we give you a referendum; we ask your opinion; we don’t like it; we’re going to ask you the same question again.

“The question you ask at the end of the deal, the end of the negotiation process, is a different process.”

He went on: “Brexit meant whatever you wanted it to mean. If you want it to mean a free market economy with no regulation and small government, then it could mean that. If you wanted it to mean an ending of influence of business in politics, it could mean that. If you wanted it to mean £350 million a week for the health service, then it could mean that.”

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But Mr Carmichael admitted that is there were a second Scottish independence referendum and the Yes camp won, then there would, on principle, have to be a third poll on the precise deal being put to Scottish voters.