The Conservatives have taken a commanding 19-point lead over Labour with less than three weeks to go before voters head to the polls, according to the latest Opinium poll for the Observer.

Poll models fail to spot voting variation in similar seats Read more

The news comes as Boris Johnson launches the Tory election manifesto on Sunday, a moment seen by many Conservative MPs as the most dangerous of the campaign. It was Theresa May’s botched manifesto in 2017, which included an unpopular social care policy dubbed the “dementia tax”, that played a major part in the collapse in her poll ratings.

The Tory share of the vote now stands at 47%, with Labour on 28% and the Lib Dems falling back to 12%. Also struggling is the Brexit party, which has collapsed to 3%. Underlying the Tory lead is the party’s success in attracting support from Leave voters: three-quarters of them say they would vote Conservative.

The results suggest that the first week of televised debates between the party leaders has not made an immediate impact on the race. Campaign chiefs at Tory HQ are now focused on avoiding the collapse endured by May two years ago by opting for a safety-first manifesto that spends significantly more money and helps the NHS, childcare and schools.

The Tory lead stood at 16 points last week, three points lower than now. However, Opinium is now taking into account the fact that some parties – primarily the Brexit party, which has pulled its candidates from Tory-held constituencies – are not running in every seat. Opinium also asked voters who they would back if all parties were running in their seat, which gave the Tories a 16-point lead – the same as last week’s poll.

The Conservative lead is now slightly bigger than at the same point before the last election, when the party held a 13-point lead over Labour. However, at that point, the Tory lead had already begun to close, falling by six points over the previous month.

Johnson, who spent yesterday campaigning with his father, Stanley, will attempt to deliver a stripped-down manifesto that focuses on extra funding and the party’s main pledge to “get Brexit done” – a slogan criticised for underestimating the amount of time and effort required to negotiate a new trade deal with the EU.

The role of the Lib Dems has now become of great interest to both the main parties. While the Conservatives were concerned that a strong performance from them could put some of its pro-Remain seats at risk, a major collapse in the Lib Dem poll ratings is likely to hugely benefit Labour.

The latest constituency-level polling by Deltapoll, published by the Observer, suggests that the Lib Dems are making inroads in specific seats, but struggling to take a lead. In the Cities of London and Westminster, Chuka Umunna is up 22 points but trails the Tories by six points. In Chelsea and Fulham, the Lib Dems are up 14 points but trail the Tories by 23 points. In Hendon, the party is up eight points but is still a distant third.