Campaigners for a second EU referendum are planning the “biggest tactical voting operation ever undertaken in Britain” in an attempt to secure a majority for another public vote.

Voters across England, Wales and Scotland will be given guidance on which candidate they should back at the next election in order to deliver a parliament willing to back a second referendum. Significant extra funds and armies of campaigners will also be directed to key seats as part of the drive to secure a new vote.

Organisers of the initiative, overseen by the People’s Vote campaign, stress it is a non-partisan project that will endorse individual pro-referendum candidates who are “best placed” to win. Among its first 20 endorsements, the campaign is asking voters to back the Lib Dem candidate in nine seats and the Labour candidate in 11 seats.

Michael Heseltine, the former Tory deputy prime minister, has backed the campaign, saying pro-remain voters would have to make a difficult choice in an election that would be “like none other”.

“The majority of people opposed to Johnson’s Brexit will have an opportunity to stop him. But this will involve difficult decisions for millions of people who may, like me in the recent European elections, find themselves voting for a party they have never backed before,” he told the Observer. “But this will be an election like none other in my lifetime. Brexit is prising loose the political allegiances of millions of people. Together, we can make sure in a new parliament there is a majority for solving this crisis.”

However, tensions are already building, with senior MPs who have campaigned against a hard Brexit among those expected to miss out on an endorsement. Anna Soubry, the Change UK MP who quit the Tories over Brexit, cited her Nottinghamshire constituency, which has previously seen a close fight between Labour and the Tories. “What are they going to do in Broxtowe? The People’s Vote campaign have to get behind the people who launched the idea of a people’s vote. We were making the case in the face of total derision from some people who are now on board. People haven’t just potentially given up their careers to back it, but also done so at huge personal cost to their safety and that of their families,” she said.

Organisers acknowledge that there will be hard cases in which “brutal” decisions will have to be taken over which candidate is best placed to win the seat. Some seats may not receive any endorsement where there is no obvious pro-referendum figure.

Facebook Twitter Pinterest Anna Soubry speaks during an event about opposing the suspension of parliament to prevent no-deal Brexit on 27 August. Photograph: Henry Nicholls/Reuters

Meanwhile, former Conservatives thrown out of the party for opposing no deal could also be supported in areas where victory for a pro-second-referendum candidate looks unlikely. In cases where the candidates with a realistic chance of victory both back a referendum, the campaign may decide only to provide information about candidates’ positions and not offer an endorsement. The project will take note of local pacts where pro-remain parties have clubbed together to back one candidate.

While immediate attention in Westminster has turned to a likely election later this year, advocates of a second referendum believe it could still prove to be the only way to resolve Britain’s EU exit. An interactive tactical voting hub will offer a “comprehensive and independent guide” to which pro-second referendum candidate is best placed to win a seat.

However, the project will focus on about 100 seats regarded as the second referendum battleground, where there is a potentially tight race between pro- and anti-referendum candidates. A provisional list of marginal seats in this battleground has been drawn up, though it is likely to change over the election campaign as more information becomes available.

Hillary Gyebi-Ababio, of the youth-led campaign group For our Future’s Sake (FFS), said thousands of students and young people had been registering to vote. “This generation of young people will be unlikely to stick to traditional party-political voting allegiances and will vote tactically.”

The People’s Vote campaign said the scheme was “the biggest tactical voting operation ever undertaken in Britain to deliver a majority in the new parliament for a final-say referendum that will give everyone the chance to decide whether the UK leaves the EU or stays”.