Dominic Raab, the foreign secretary, is in danger of providing this election’s “Portillo moment”, after a poll in his constituency suggested that he was at risk of losing his seat.

Could tactical voting result in a ‘Portillo moment’ for Dominic Raab? Read more

The Deltapoll survey of Raab’s Esher and Walton constituency indicates he now only holds a five-point lead over the Liberal Democrats with less than two weeks before voting. Yet Raab had a massive 23,298 majority at the last election. The fact the foreign secretary faces a close race shows there could be big swings in some seats, and means Raab is vulnerable to a so-called “Portillo moment” – a reference to the shock defeat suffered by Michael Portillo in the Labour landslide of 1997.

Meanwhile the penultimate pre-election Opinium poll for the Observer suggests the Tory lead has fallen. The Conservative lead has dropped to 15 points from 19 points, with Labour gaining three points since last week. The Conservatives are down 1 point to 46%, while Labour has climbed to 31% of the vote share. The poll finds that about 16% of eligible voters are not sure which party they will vote for.

Of those undecided, half are considering voting for the Conservatives, while 29% are considering Labour. More than a third of undecided voters will not make up their minds on who to vote for until election day. And health is the issue most likely to decide their vote, they said.

Opinium said the Leave vote was still coalescing behind the Conservatives, with the party holding 76% of the group, up 1 point from last week. Labour has seen a small increase in the last week, gaining 3 points to hold 14% of the Leave vote.

The Brexit party is down 3 points to an all-time low for the party of 3% of the Leave vote share.

In an online article for the Observer, Ian Lavery, the Labour party chairman, attempts to persuade traditional Labour voters tempted by the Tories to stick with his party. He calls on them to think about “whose side you’re on”. Lavery states that he will campaign for Britain to leave the EU with a new deal secured by Labour, should the party win the election and hold a second referendum. “I’m no fan of a second referendum,” he writes. “But politicians have failed to find a way through this mess.

Facebook Twitter Pinterest Michael Portillo, right, after losing his Enfield Southgate constituency, 2 May 1997, to Labour’s Stephen Twigg, left. Photograph: Kevin Lamarque/Reuters

“Labour’s policy seeks to draw to a close the endless wrangling in Westminster by securing a new deal, along the lines we set out in 2017 and asking you to decide. It is no secret that I would campaign to leave the EU with a Labour deal, but it would be up to you.

“Getting a final decision on Brexit within six months and implementing it immediately would free up the political space to tackle the real issues in our society.” However, he also urges voters not to make the election about Brexit. “After almost a decade in power with Britain in chaos [the Tories] are desperately trying to make the election about one thing. Brexit,” he writes. “This election isn’t and shouldn’t be about Brexit. It’s about the kind of country we want to live in.

“This election there is a choice. Which side are you on? An ignorant elite, educated beyond their intelligence, the bad bosses, the big polluters, the dodgy landlords, the tax avoiders? Or the many? The choice is simple.” Opinium polled 2,018 people between 27 and 29 November.

The Deltapoll constituency-level polling put the Tories on 46% in Dominic Raab’s constituency, with Lib Dems on 41%, and suggested Labour voters were switching to Monica Harding, the Lib Dem candidate, while pro-Remain Tories were deserting Raab. When Deltapoll asked how people would vote if they saw it as a contest between the Tories and Lib Dems, the two parties were tied at 48%.

The constituency polling showed just how much party fortunes could vary. In places such as Portsmouth South and Berwick-upon-Tweed, two former Lib Dem seats, the polling suggested Jo Swinson’s party has little chance of winning.

The polling also suggested former Tory independents David Gauke and Dominic Grieve would struggle to retain their seats. Deltapoll questioned 500 electors in each constituency by telephone between 21 and 28 November.