Some 72% of Britons lack confidence in her ability to reach a good deal with Brussels, the worst rating the Prime Minister has had in the Ipsos MORI political monitor.
Her personal approval rating also hit a new low over the past month, with Mrs May achieving a net score of minus 32.
Some 30% say they are satisfied with the way Mrs May is doing her job as Prime Minister, down five points since June, and 62% dissatisfied, up four.
Jeremy Corbyn had a net score of minus 30, according to the survey for the Evening Standard, with 28% satisfied in his leadership and 58% dissatisfied.
Only 29% of those surveyed said the Prime Minister’s Chequers Brexit blueprint would be a good thing for the UK, with 47% suggesting it would be bad and 19% saying they did not know.
The two main parties are running neck and neck in voting intention figures, with both the Conservatives and Labour on 38%, the Liberal Democrats on 10% and Ukip on 6%.
Gideon Skinner, head of political research at Ipsos MORI, said: “Theresa May has faced a lot of criticism since she launched her Chequers deal, and our poll for the Standard shows this is mirrored among the public, with her ratings continuing their recent decline to another new low (and the fall has been even sharper among her own supporters).
“But despite all that, our trends show her ratings are not unusual for a prime minister two years in, and are still better than many of her potential alternatives.”
- Ipsos MORI interviewed a representative sample of 1,023 adults by telephone on July 20 to 24.