The campaign leading the push for a second EU referendum has drawn up a hit list of 100 marginal seats in which it will tell Remain supporters to vote tactically at an early general election. The aim is to boost the number of MPs who favour putting the Brexit issue back to the people.

The People’s Vote campaign is planning to blitz marginals across England, Scotland and Wales before a widely expected early poll, urging Remainers to ditch their traditional party loyalties where necessary in order to help install pro-referendum MPs or defeat MPs or candidates who oppose a second public vote.

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Supporters of another referendum believe that if they can boost the number of MPs who support putting the issue back to the people, they can then win a Commons vote to trigger a second vote and reverse Brexit.

An internal strategy paper written by the director of the People’s Vote campaign, James McGrory, predicts that “tactical voting will be a bigger factor than in any previous election fought in the UK”. It says that while alliances between Remain parties may be formed in some areas and be helpful, his organisation’s priorities will be “more about individuals than political parties”.

Facebook Twitter Pinterest The tactical voting campaign will also seek to protect supporters such as Layla Moran, who holds Oxford West and Abingdon by only 816 votes. Photograph: Greg Blatchford/Rex Shutterstock

Key seats in the PV100 target list include Richmond, where the pro-Brexit Tory MP Zac Goldsmith has a majority of 45 over the Lib Dems; Chingford and Woodford Green, where the former Tory leader Iain Duncan Smith has a majority of only 2,438 over Labour; and Chipping Barnet, which Theresa Villiers, the secretary of state for environment, food and rural affairs, won at the 2017 election by just 353 votes over Labour.

The PV campaign will also fight to defend pro-referendum sitting MPs including the Liberal Democrat Layla Moran in Oxford West and Abingdon, who ousted the Tory Nicola Blackwood by just 816 at the 2017 general election.

McGrory says campaign structures and teams will be set up for all the seats, and that voters will be targeted digitally. “In some cases we will be asking Labour supporters to vote for other parties such as the Liberal Democrats. In many others we will be asking supporters of the Liberal Democrats, the Greens or others to vote Labour. This is based on nothing more than the hard-headed acknowledgement of which party is best placed to beat an opponent of the people’s vote,” he said.

“In marginal seats where the Labour candidate does not support a people’s vote on any Brexit outcome, we will not give our backing. But we recognise that we will be asking some of our supporters to ‘hold their noses’ and vote for a party they dislike. We hope this will be a one-off based solely on the importance of securing a democratic people’s vote on the most crucial issue of our generation.”

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Boris Johnson has insisted he is not planning an early general election before the UK is due to leave the EU on 31 October. But many MPs believe that the prime minister will call one early next month if he cannot secure an improved deal with the EU, and use it to ask the British for a mandate to take the country out without a deal.

Johnson’s Commons majority was cut to one last Thursday when the Lib Dems ousted the sitting Tory MP, Chris Davies, in the Brecon and Radnorshire byelection. The Lib Dems were helped over the line by the Greens and Plaid Cymru, who did not put up candidates so as not to split the Remain vote.

While similar Remain alliances are likely to be formed in some areas at a general election, neither Labour nor the SNP is prepared to stand down candidates, meaning such agreements will be limited in number, and decided informally according to local circumstances.