The poll puts the Tories on 42%, down one point on the last YouGov figures on Friday.
Labour is on 33%, down one point, the Liberal Democrats are on 12%, also down one point, and Brexit Party is on 4%, up two points.
The Conservative lead is unchanged from last week, with all changes within the margin of error.
The election campaign has seen a small shrink in the Tory lead, even though Boris Johnson's party are comfortably ahead.
There is evidence that people who voted Labour in 2017, but were sceptical at the start of the campaign, have come round to supporting Jeremy Corbyn's party over the last month.
The first YouGov poll for Sky News, at the start of November, found that only 57% of 2017 Labour voters who know who they are voting for were going to choose Mr Corbyn's party.
This figure has now increased to 71%, and there has not been a corresponding change among 2017 Tory voters.
The poll also found the Conservatives are losing ground in terms of convincing people they reflect the best interests of voters.
Asked which party reflect the views of respondents the most, 25% said the Tories, 23% said Labour, 10% said the Lib Dems and 7% said the Brexit Party.
The Tories previously enjoyed a five-point lead over Labour on this question.
YouGov interviewed 1,699 GB adults on Monday and Tuesday.
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