Jeremy Corbyn put honesty and integrity – the idea of doing politics in a different way – at the heart of his pitch for the Labour leadership four years ago. That makes Labour’s long-standing failure to clarify whether or not it is decisively in favour of a confirmatory referendum on any Brexit deal all the more depressing.

Ambiguity remains the name of the game as we approach the European elections in just a few weeks. A draft campaign leaflet that was leaked last week did not even mention a referendum, pledging that Labour would seek “a better deal with Europe” after Brexit. Andrew Adonis, now a Labour MEP candidate in the south west, was apparently required to put out a clarifying statement, after breaking party rules last September by telling Brexit supporters they should not vote Labour. “Labour has always been clear that it respects the result of the referendum,” wrote the Labour peer, who has been an ardent supporter of a second referendum. “Labour has put forward a sensible alternative plan that would ensure a close economic relationship with the EU after Brexit.”

More than 90 MPs and MEPs have rallied behind a demand for the party to unambiguously adopt a confirmatory referendum on any Brexit deal as its firm policy going into the European elections. They have written to Corbyn urging him to pledge a referendum before the meeting this Tuesday of the party’s national executive committee, which will approve its European elections manifesto.

Facebook Twitter Pinterest Labour’s deputy leader, Tom Watson, at a People’s Vote rally in March. Photograph: Isabel Infantes/AFP/Getty Images

Time is running out. As Labour’s deputy leader, Tom Watson, argued in the Observer , Labour must embrace a referendum on any Brexit deal. The democratic case for a referendum, which the Observer first made more than two years ago, remains as strong as ever. Voters were not offered a firm proposal for leaving the EU in 2016; instead, they were made false promises that Brexit would involve Britain seizing back control, the freeing up of vast sums of cash for public services and a significant boost for the economy. Now there is a firm deal on the table and it embodies all the difficult trade-offs Brexit must involve, including the reality that there is no way of achieving a clean break from the EU that respects the Good Friday agreement. It would be unthinkable for parliament to vote for it without putting it to voters for ratification.

There is no majority in favour of any Brexit option: not a soft Brexit, not May’s withdrawal agreement, not no deal

Moreover, parliament remains gridlocked. There is no majority in favour of any Brexit option: not a soft Brexit, not Theresa May’s withdrawal agreement, not no deal. The only way out of this stalemate is for MPs to put the exit deal that has been negotiated to voters.

Corbyn claims to be committed to party democracy: if so, backing a referendum is the only thing to do. According to Watson, an overwhelming majority of MPs back a referendum. And 72% of the party membership think the leadership should swing its weight behind another referendum. Every large affiliated union, bar Unite, backs a referendum. The international commission of Labour’s national policy forum, which includes trade unionists, MPs and constituency representatives, has voted unanimously that Labour’s European elections manifesto should pledge to hold a confirmatory referendum.

It is also in Labour’s own electoral interests. Three-quarters of Labour voters think Britain was wrong to leave the EU. Polling suggests that Labour will lose votes to the Lib Dems and other referendum-supporting parties if it goes into the European elections appearing to support any type of Brexit.

This week, Labour has to choose between backing a referendum or continuing to say its favoured option is a soft Brexit. With no failsafe way of triggering a general election, the only way Labour can deliver on the latter is through a compromise with May. That’s fraught with danger; there are no guarantees she can offer that would be binding on her successor’s negotiations with the EU about our future relationship. It’s now or never time for Corbyn. What does Labour stand for?