Labour activists campaigning to stop Britain leaving the EU single market have vowed to fight on after being denied a vote on changing their party’s policy, in a bitter row.

MPs pledged to take their argument “to every constituency Labour party in next 12 months”, to keep pressure on Jeremy Corbyn and the rest of the leadership to change course.

Alison McGovern, one the campaign’s leaders, told The Independent: “If we can’t talk about it at Labour conference, then we will talk about it around the country, so people can have their say.

“Clearly, there is an appetite among Labour members for this – and we will be seeking to bring that about.”

Chuka Umunna, one of 30 Labour MPs who signed an open letter to Mr Corbyn, added: “We will continue to make this argument.”

The pledges came after an attempt to force a rethink of Labour’s overall Brexit approach was comfortably defeated in the conference hall in a show of hands.

The victory for the leadership came after accusations of a backroom “fix” to prevent motions on permanent single market membership and continued freedom of movement being debated.

John McDonnell, the Shadow Chancellor, rejected the charge, insisting delegates had selected the priority motions for debate and – in rejecting Brexit – had shown “democracy at work”.

Despite the row, pro-EU Labour MPs were buoyed by a statement that their party is likely to support staying in “a form of customs union” after Brexit.

In his conference speech, Sir Keir Starmer, the Shadow Brexit Secretary, said: “Options for achieving that end should not be swept off the table.

“Subject of course to negotiations, remaining in a form of customs union with the EU is a possible end destination for Labour.”

Meanwhile, a new survey revealed a continued pro-EU shift among Labour voters, which is likely to pile further pressure on Mr Corbyn to respond.

A narrow majority now supports a further referendum that would see Britain stay in the EU if the alternative option – accepting any Brexit deal on the table – is rejected.

Overall, 70 per cent of Labour voters now want some form of second referendum, which could include an option of sending the Government back to the negotiating table, the pollsters GQRR found.

In Brighton, the party’s ruling NEC committee attempted to paper over Labour’s divisions by issuing a statement that tried to turn the focus on the Tories for “whipping up” hostility against immigrants.

However, it backed membership of the single market and the customs union only during the “transitional period” that both Labour and the Conservatives now advocate.

And it stated: “Labour campaigned to remain in a reformed European Union, but as democratic socialists we accept and respect the referendum result.”

Later, Sir Keir raised eyebrows by saying he rejected the idea that Britain’s new relationship with the EU had to be worse than before withdrawal.

He told a fringe meeting: “I have a six-year-old girl and a nine-year-old boy, and I’m not going to let them grow up with their dad saying to them that it’ll never be as good as it was.”

Tom Brake, the Liberal Democrats’ Brexit spokesman, accused Labour of “joining the Tories in the land of fairy tales”, adding: “Labour should be fighting with the Liberal Democrats to maintain membership of the single market and customs union.”