Analysis commissioned by the publication looked at the seat as one of five constituencies The Economist has asked for polling for ahead of the December 12 General Election.
It found the Conservatives and their candidate, councillor Lia Nici, were on 44 per cent, a full 13 points ahead of Labour in the area, whose vote has collapsed since 2017.
And it could mean Boris Johnson is set to take the Labour stronghold as the PM put a laser-focus on Leave-voting Labour seats in the North.
The analysis found Labour’s vote had fallen from 49 per cent in 2017 to just 31 per cent now, while the Brexit Party were also doing less well than expected, on 17 per cent.
Lia Nici, the Tory candidate for the seat, said: "Everyone was very excited about the poll but I will only believe it if I get elected.
"It is looking very positive on the doorstep with a lot of people who are saying they are going to vote Conservative for the first time and we’re coming across very few Brexit Party voters. I just need to keep meeting people and hopefully they will see that I will be a hard working MP if elected on the 12th."
But Mel Onn, Labour’s MP for Great Grimsby until the election was called, said this was not the impression she was getting on the doorstep - and said Tory voters were switching to Labour.
Ms Onn, who is running again, said: “The poll is very narrow and does not reflect the conversations our Labour supporters have been having with Grimsby people.
“A surprising number of lifelong Conservative voters are looking for an alternative, appalled with Boris Johnson cosying up to Nigel Farage so blatantly.”
She added: “There is still a way to go before election day and the only poll that really matters is the one on 12 December.”