Jeremy Corbyn has given up trying to hold the government to account on its plans to leave the EU, Tim Farron has said.
The Liberal Democrat leader issued the withering remarks at the party’s conference in Brighton, ahead of an expected endorsement by the membership of plans to hold a second referendum on the terms of the final deal.
"Jeremy Corbyn has already thrown in the towel,” Farron said.
“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.
"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.”
Corbyn’s team were criticised earlier this month when his spokesman repeatedly refused to confirm whether the Labour leader wanted Britain to stay in the single market.
Leaving the single market, which is the aim of most prominent Conservative Brexit supporters, would free Britain from freedom of movement rules and end any payments to Europe.
But it would also mean the return of tariffs to exporters sending shipments to the continent, which would have a devastating impact on manufacturing, particularly in the car industry.
And experts believe a significant reduction in immigration would have a damaging effect on Britain’s economy and its debt-to-GDP ratio.
Corbyn has long considered the single market a capitalist invention, whose restrictions on state aid rules make it difficult for governments to nationalise or even prop up failing industries.
Opponents of a second referendum on Brexit, which is also supported by Corbyn’s leadership challenger Owen Smith, say the plan is a way to sidestep the referendum result, but supporters believe it is a way to ensure voters support the terms of a final deal which could have a serious impact on their living standards.
"Voting for a departure is not the same as voting for a destination,” Farron said.
“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.
"In the meantime we will fight for the best deal possible - and that means the single market. Nothing is more important to Britain's economic future. Nothing will make more difference to British jobs and British businesses.”
The government’s broad proposals for delivering on Brexit are expected to be made public in the early part of next year, shortly after Theresa May triggers the Article 50 process.