Labour now has the support of 50% of voters and has surged to a 25-point lead over the Conservatives, according to a new poll.
It will be a blow to Rishi Sunak and a boost to Keir Starmer after a difficult August for the prime minister.
The Deltapoll survey put Labor on 50%, the Tories on 25%, the Lib Dems on 9% and other parties on 17%.
Sunak has to call a general election by January 2025 at the latest, but it is widely assumed he will go to the country next year.
The poll was conducted between August 17 and 21 and showed Labour jumping 4-points and the Conservatives dropping 4-points since the previous survey, which was run from August 9 until 11.
According to the pollster, it means Labour has widened its lead over the Tories by 8-points.
The government had hoped to use the second week of August to take the fight to Labour on migration and the NHS.
But “small boats week” backfired when asylum seekers being housed on the Bibby Stockholm barge were removed after the Legionella bacteria was discovered on-board.
Sunak has also admitted he may not meet his pledge to “stop the boats” by the next election.
And “health week” - which followed - was consumed by a row over waiting times for cancer patients.
There was better news for the prime minister last week however, when the latest figures showed inflation dropped to to 6.8% in the year to July from 7.9% in June.
The PM has promised to half inflation from its peak of 10.7% at the start of the year.
Officials statistics also showed UK wages had grown at a record rate in the three months to June.