More than 100 constituencies which backed Leave in the 2016 referendum would now vote to remain in the European Union, according to new analysis of polling.
The findings suggested that most seats in England, Scotland and Wales now contain a majority of voters who want to stay in the EU.
The analysis, obtained by The Observer, suggested the development was driven by growing doubts about the case for Brexit particularly among Labour voters in the north of England and Wales.
The findings will heap pressure on Labour leader Jeremy Corbyn to reconsider the party's refusal to give its backing to a second referendum on EU membership.
Even though polls regularly report a strong lead for Remain among Labour voters, a majority of the party's constituencies backed Brexit in 2016, leaving party strategists wary of any suggestion that it might not deliver withdrawal.
The figures were produced by consumer analytics company Focaldata, drawing on two YouGov polls of a total of more than 15,000 people.
They found that 112 out of the 632 seats in England, Scotland and Wales had switched from Leave to Remain since the referendum. These included 97 English seats, 14 in Wales and one in Scotland.