Campaigners for a referendum on the Brexit deal are promising the “biggest ever pro-European march”, as their hopes grow for a fresh public vote.

The demonstration – to be staged on the second anniversary of the Leave vote in June – will kick-start a “summer of action and mobilisation”, they say.

Supporters of giving the people a “final say” on the exit deal negotiated by Theresa May expect to attract huge numbers from across the UK and as far afield as Gibraltar.

The march, on 23 June, comes after the government acknowledged that MPs have the power to force a new referendum by amending a vote on the withdrawal agreement in the autumn.

Steve Baker, the Brexit minister, said the crucial vote would not – as expected – be a “take it or leave it” choice, because “parliament can always seek to amend motions”.

Now the March for a People’s Vote will, for the first time, bring together ten major pro-EU campaigning organisations under the same banner, through central London.

James MacCleary, of the European Movement UK, one of the groups behind the campaign, urged people to join the march to “make such a noise about it that is so loud it will be impossible to ignore.”

Femi Oluwole, of Our Future Our Choice, said: “Young people have the most at stake here and, if we leave the EU in March 2019 without a People’s Vote, half a million young people will have been denied any say about the biggest decision on their future.”

And James McGrory, of Open Britain said: “Brexit will affect everybody in the country, which is why it should not be left to 650 politicians in London to decide our future but to all 65m people. That is why so many are demanding a People’s Vote on the final Brexit deal.”

The campaign has launched a crowd funding appeal to raise £100,000 to meet the costs of organising and advertising for the march.

Ms May has firmly rejected a further referendum, but some pro-EU Tories believe she could yet accept one if it appears the only way to keep her warring party together on Europe.

Similarly, although Jeremy Corbyn has said Labour does not back another referendum, he has left the door open to a change of mind.

There is also polling evidence that public support is growing for a referendum on the Brexit deal, amid continuing confusion about both the planned transition period and the final trade deal with the EU.

Opinion appears to be shifting as the negotiations remain bogged down on how to avoid a hard border in Ireland and with the details of a trade deal unlikely to even be discussed until after departure day.

Some Tory MPs also believe a legal challenge – to require a further referendum before Brexit can go ahead – could yet put the government in difficulty.

The case will argue that the 2011 “referendum lock” introduced by David Cameron – preventing any significant change to relations with the EU without the public’s say – applies to the Brexit talks.