Other polls in recent days have given the Conservatives a lead of between 10 and 15 points but the BMG survey suggests this has been cut significantly after a week that was widely seen as positive for Labour.
A series of big policy announcements, including a promise of free high-speed broadband for every home and business, helped Mr Corbyn’s party to dominate the agenda, while the Tories were forced onto the defensive over new figures revealing that A&E waiting times are the worst in almost a decade.
Despite their lead narrowing when compared to other polls in recent days, the Tories are still in a stronger position than a month ago, the survey suggests, before Mr Johnson secured his new Brexit deal. A similar BMG survey at the time gave them only a 5-point lead.
Pollsters say that a lead of around 10 points over Labour would be needed to guarantee Mr Johnson a majority.
BMG said it had adjusted the poll to account for rates of electoral registration among different groups of voters. Without this, it said, the Tories’ lead would have been reduced even further.
Mr Johnson’s advantage appears to be partly due to his success in uniting Leave voters behind him after Nigel Farage announced that his Brexit Party would not field candidates in seats that the Tories are defending.
Some 61 per cent of Leave voters now say they will back the Tories – a big leap from the 48 per cent who said the same last month.
In a similar trend, Labour is picking up more Remain voters. While last month 37 per cent of people who backed Remain in 2017 said they would vote for Mr Corbyn’s party and 32 per cent said they would support the Liberal Democrats, the figures are now 40 per cent and 28 per cent respectively.
Further cause for optimism for Mr Johnson comes from a finding that he is still significantly more popular than his Labour counterpart, with voters preferring him to Mr Corbyn as prime minister by a margin of 39 per cent to 24 per cent.
Overall, Mr Johnson has a net satisfaction rating of -12, while Mr Corbyn’s is -43. Lib Dem leader Jo Swinson is on -18.
The poll also found one of the biggest ever majorities against Brexit, with 54 per cent of people now saying the UK should stay in the EU, compared to 46 per cent who still want it to leave.
Robert Struthers, head of polling at BMG Research, said: “With Labour’s poll rating improving slightly over the last few months, so too have perceptions of Corbyn’s own performance. This is not to say that the Labour leader should now be considered a popular leader, but he has recovered from a low of -48 per cent in July, rising to -36 per cent in this poll. That being said, the Labour leader remains significantly less popular now than he was one month out from the 2017 election where we recorded his net satisfaction at -17 per cent.”
He continued: “Boris Johnson continues to hold a considerable advantage over Jeremy Corbyn in terms of personal approval ratings, with two in five preferring Johnson as the next prime minister, which compares to just a quarter who back Mr Corbyn.
“One reason for this lead is the fact that many of those who backed Labour in 2017 do not appear comfortable with the idea of the Labour leader entering Downing Street. Three in 10 of those who reported backing Labour in 2017 say they would prefer neither Corbyn nor Johnson to become prime minister, with a further 15 per cent saying they would prefer Johnson over Corbyn.”
BMG Research interviewed a representative sample of 1,506 British adults online between 12 and 15 November. Data are weighted. BMG are members of the British Polling Council and abide by their rules. Figures have been adjusted to account for rates of electoral registration among key groups.
This poll was conducted during a week in which the Brexit Party confirmed that it would not stand in constituencies that the Conservatives won in 2017, meaning that respondents will have been able to select the Brexit Party despite living in seats where they are not standing. Future BMG polls, conducted after the deadline for nominations has closed, will include constituency-level candidate information so each respondent is only able to choose from a list of parties who are confirmed as standing.