Dominic Raab’s fierce enthusiasm for Brexit could cost him dear in a constituency that voted Remain in the 2016 referendum.

His 23,298 majority in Esher and Walton at the last general election was one of the largest in Britain. In normal times, defeat would be unthinkable. Yet he now faces a pincer movement, with Labour supporters switching tactically to Monica Harding, the Liberal Democrat candidate, and almost half of the 12,000 Remain voters who backed Raab two years ago now plan to desert the foreign secretary.

Dominic Raab in danger of losing seat to Lib Dems, poll finds Read more

On the conventional voting intention question, Raab clings to an uncomfortably narrow five-point lead. But when Deltapoll asked voters how they would vote if they thought only the Tories and Lib Dems had a realistic chance of winning the seat, Raab and Harding tied at 48% each. It’s possible, then, that Esher will provide the “Portillo moment” on election night – the defeat of a high-profile cabinet minister on a huge swing. The difference is that in 1997 Portillo was just one of many Tory victims in Tony Blair’s landslide. This time, Raab might lose his seat while his party piles up gains elsewhere.

Deltapoll’s latest batch of constituency surveys demonstrates the extraordinary seat-by-seat variations that we are certain to see on election night. The Tories seem likely to fend off challenges from Dominic Grieve and David Gauke, former ministers now standing as independents. Historically, MPs elected on a party ticket seldom retain their seat as independents. That pattern looks set to continue.

Beaconsfield, where the Liberal Democrats have stood down, is effectively a straight fight between Grieve and Joy Morrissey, his successor as the Conservative candidate. With Labour’s support down to just 7%, tactical voting could halve Morrissey’s lead to nine points but not wipe it out. To win, Grieve must win over most of the 6,000 Remain voters who currently plan to vote Conservative.

Gauke’s challenge is even tougher. He has similar support to both Labour and the Liberal Democrats, who decided not to stand aside in Herts South West. Had they done so, Gauke would almost certainly now be a clear second, with an outside chance of picking up enough tactical votes to challenge Gagan Mohindra, the Conservative candidate. That now looks unlikely.

The two other seats polled last week were among the 49 that the Lib Dems lost in 2015. One route back for the party would be to regain some of these seats. The results from Berwick and Portsmouth South will give them little comfort. They are currently second in Berwick and a distant third in Portsmouth South, with the Tories well ahead in Berwick and Labour leading more narrowly in Portsmouth South.

Berwick was held by Sir Alan Beith for more than 40 years and built up a big personal vote. He has gone and that personal vote has evaporated. Berwick now looks like the standard, rural Tory stronghold it used to be.

Portsmouth South, uniquely in England, installed MPs from different parties at each of the last three elections: Lib Dem in 2010, Conservative in 2015, Labour in 2017. It is now quite clearly a Labour-Conservative contest, with Lib Dem support down to just 11%. At present, Labour’s Stephen Morgan is on course to double his 1,554 majority. However, that means it remains a marginal that the Tories could still capture.

Taken together, these findings suggest a wider point. National polling figures show that support for the Lib Dems has faded during the current campaign. But their fortunes vary hugely from seat to seat. Deltapoll has surveyed 11 constituencies in the past three weeks. The Conservatives are defending 10 and currently lead in all 10. But tactical voting could deliver five of them to the Lib Dems: Kensington, Finchley and Golders Green, Wimbledon, Cities of London and Westminster, and Esher and Walton. Jo Swinson’s future, and just possibly Boris Johnson’s, could depend on the extent of tactical voting on 12 December.

• This article was amended on 6 December 2019. As the graphic on current voting intention showed, the Lib Dems were a distant second in Berwick, not a distant third.

Peter Kellner is a polling expert and former president of YouGov