Tom Watson is urging grassroots members to sign up to a public declaration calling for Labour to be “the party of remain”, as pressure mounts on Jeremy Corbyn to embrace an anti-Brexit position.

In a move likely to be regarded as provocative by Corbyn’s team, Watson is publishing a statement online, and inviting signatures, to underline the breadth of concern about Labour’s stance.

“As the party of remain, we will not take every voter with us, but it’s the only way that Labour can win, and the only way to keep our country together,” the statement says.

Since the party’s disastrous performance at the European elections in May, winning just 14% of the vote, Labour’s position has already evolved.

Corbyn has repeatedly said, including in the House of Commons, that any Brexit deal – or a no-deal Brexit – should be put to a public vote.

He told Theresa May last week: “Whoever the next prime minister is, they will barely hold the support of this house, so they certainly have no mandate to force a disastrous hard-right Brexit on this country. Whatever Brexit plan the new Tory leader comes up with, after three long years of failure they should have the confidence to go back to the people on a deal agreed by parliament.”

But Watson is among those members of the shadow cabinet who would now like to see Corbyn go further, and commit his party to campaigning for remain in a second referendum.

Some of Corbyn’s closest allies, including Diane Abbott and John McDonnell, have also said they want to see a shift, with the issue cutting across the traditional left-right divide within the party.

Corbyn has insisted that he is still consulting on the issue; and has privately pointed to the historical lessons of the Harold Wilson government.

Wilson formally backed continued membership of the European Community in the 1975 referendum; but took a back seat during the campaign, and allowed his cabinet to campaign on opposing sides. One of those then urging a leave vote was Corbyn’s lifelong political hero, Tony Benn.

Corbyn’s spokesman has said a firm position is likely to be reached before MPs leave Westminster for the summer recess later this month.

If the new stance is not resolutely anti-Brexit, Labour campaign groups including Love Socialism Hate Brexit are readying themselves for a summer of action before the party’s conference in September.

It was last year’s conference in Liverpool where the “composite motion”, which first put the option of a referendum “on the table” as part of Labour policy, was hammered out.

But a number of MPs and members of the shadow cabinet, including Jon Trickett and Ian Lavery, continue to have profound concerns about the party embracing a remain position.

They point out that the Brexit party represents a threat to Labour, as well as the anti-Brexit Lib Dems. A YouGov poll for the Times this week put Labour in fourth place behind both those parties, and the bitterly-divided Conservatives, on 18% of the vote.

Watson’s statement says: “Labour’s democratic tradition confers on us an obligation to win elections. Without power we can achieve nothing. As a party of Brexit we will never win again, and that is an abrogation too far.

“Because we love Britain, and because we believe in Labour, we will fight, fight and fight again to keep Britain in the EU. The next step, which only Labour can deliver, needs to be a public vote on the Brexit fiasco, with Labour leading the way for remain.”

It goes on to say “a democratic socialist Labour government – equality, social justice, opportunity and prosperity for all of Britain – will follow swiftly when we regain the people’s trust.”