The Liberal Democrats have vowed to fight on to retain single market membership after Brexit, after Labour was accused of throwing in the towel.

Tim Farron, the Lib Dem leader, said he would table an amendment to the Article 50 legislation to try to stop Theresa May pulling out of the EU trading arrangements.

The demand will be in addition to the party’s ‘red line’ – that voters must be given their say on the final deal that emerges from the talks, in a referendum.

Labour was accused of a U-turn yesterday, when it appeared to drop a vow to try to force the Government to commit, in law, to tariff-free access to the single market.

Later, that proposed amendment was removed - because, the party said, the Article 50 Bill would be about the “process of Brexit”, rather than “negotiating objectives”.

But Mr Farron said the Lib Dems would table an amendment, arguing single market membership remained crucial to Britain’s economic prospects.

He told BBC Radio 4’s Today programme: “Membership is totemic and also substantial – in many ways it marks the difference between a hard and soft Brexit.

“Membership of the single market is something that many non-EU countries have and it’s clearly in the interests of our economy

“The Government should be negotiating from a starting point that we stay in, so we will try to push them into that position.”

A referendum on the eventual deal – and the option for voters to stay in the EU – was essential to prevent “a stitch-up between Whitehall and Brussels over the content of our new relationship with Europe”, Mr Farron said.

“We take the view that the vote in June was a vote for departure from the European Union. It was not a vote for destination,” he added.

However, Labour has said it does not support a further referendum, after insisting it will not obstruct Brexit because of the original referendum result.

Instead, its focus will be an attempt to force Ms May to go back to Brussels to seek a better deal if her exit terms are rejected in the Commons, probably in 2019.

The Prime Minister has issued a ‘no deal is better than a bad deal’ threat – insisting MPs voting against her terms would mean crashing out of the EU with no agreement at all.

On the single market, meanwhile, Ms May has argued membership is incompatible with her ‘red line’ which is to restrict EU immigration.

Despite its stance on a further referendum and the single market, Labour has threatened to wage “hand-to-hand combat” with the Government over Brexit.

Shadow foreign secretary Emily Thornberry said Labour would – in alliance with pro-EU Tory rebels - insist on a white paper setting out Ms May’s proposals in detail.

“Article 50, if it is going to be triggered, we will not get in the way of it, but we will try and amend the legislation in order to ensure that they keep coming back, that we keep an eye on them,” Ms Thornberry said.