The new score is down 10 points from late November, the pollster said on Wednesday, adding that the prime minister's popularity slipped amid the government's efforts to curb irregular migration into the country.
Sunak's favorability rating came close to that of former UK Prime Minister Boris Johnson, whose score was -53 points at the time of his resignation, according to the poll.
Meanwhile, UK opposition Labour Party leader Keir Starmer's net favorability rating was not much higher than Sunak's one. Only 32% of respondents have a positive opinion of Starmer compared to 54% with a negative one, the poll showed.
The survey was conducted among 2,000 adults from December 11–12.