A small number of Reform voters in constituencies across the country could prevent Sir Keir Starmer winning a Labour landslide if they switch to back the Conservatives.
Analysis of data from a ‘mega-poll’ suggests that the Conservatives are neck-and-neck with Labour in dozens of seats.
The survey of 10,850 voters by More in Common last week forecast that Sir Keir is on course for a landslide majority of 162, with the number of Tory seats slashed by more than half to 155.
The think-tank found there were 96 seats in which the Conservatives were within five points of Labour.
If the Tories won all of them, then the total number of the party’s seats would jump to 203, cutting Labour’s majority and providing a platform for the Conservatives to provide an effective opposition to Sir Keir.
Analysis of the data by the Mail suggests that in many areas the Conservatives could win with just a small swing from Reform.
In seats as far afield as Plymouth Moor View, in Devon, and Morecambe and Lunesdale, in Lancashire, the Conservatives are just a handful of points behind.
In others, Brexiteers and immigration hardliners are within a whisker of being ousted by Labour MPs if disaffected Tory voters gamble on backing Reform.
Former immigration minister Robert Jenrick, a potential Tory leadership contender who resigned to push for tougher border controls, is forecast to fall two points short of Labour in Newark, where Reform is polling more than 10 per cent.
In Harwich and North Essex, veteran Brexiteer Sir Bernard Jenkin is less than a point behind his Labour rival.
Elsewhere, in seats like Bracknell and the Derbyshire Dales, a narrow lead could be hauled in by Labour with only a tiny swing unless Tory supporters lending their votes to Reform return to the fold.
In other parts of the country, the Conservatives need to claw back support from Reform to win against pro-EU parties such as the Liberal Democrats and SNP.
In West Aberdeenshire and Kincardine, energy minister Andrew Bowie is forecast to fall less than one per cent short of holding off the SNP, who want to break up the UK and take Scotland into the EU.
Brexiteer Derek Thomas is also forecast to be less than 1 per cent behind the Lib Dems in St Ives, in Cornwall, where Reform are polling more than 10 per cent.
A separate mega-poll by YouGov last week suggested Labour was on course for a 200-seat majority with 39 per of the vote.
The predictions underline the importance for the Tories of galvanising the centre-Right vote in order to provide a competitive challenge to Labour.