Keir Starmer has suffered a precipitous fall in his personal ratings since winning the election, according to a new poll for the Observer that comes before his first Labour conference as prime minister.

The latest Opinium poll reveals that Starmer’s approval rating has plunged below that of the Tory leader Rishi Sunak, suffering a huge 45-point drop since July. While 24% of voters approve of the job he is doing, 50% disapprove, giving him a net rating of -26%. Sunak’s net rating is one point better.

The prime minister is not alone in suffering from a major drop in personal support since the election. Rachel Reeves, the chancellor, who has cut winter fuel payments for all but the poorest pensioners and promised tough decisions on welfare and tax in the forthcoming budget, has seen a 36-point drop in her net approval since July.

While Labour continues to lead on most issues, it has almost lost its lead on the economy. It is ahead by only one point on the issue, down from a 10-point lead in July. A third see the government as being open about the challenges facing the country, but more than half think the government has been bad at providing optimism or rebuilding trust in politics.

It suggests any honeymoon for the new government is over, with falls in approval ratings across the board for the senior figures in the cabinet. Almost half of the public (45%) now have a more negative view of Starmer and Labour since they came into office. However, the last Conservative government is still seen as the most to blame for the challenges facing the government.

In a troubling assessment of the government’s opening months, only 27% think it has so far been a success, while 57% think it has not been successful. Even a third (32%) of those who voted for Labour at the last election believe the government has not been a success in its opening two months. Labour is seen as focusing too much on the government’s fiscal position when the public want them to focus on growing the economy.

James Crouch, head of policy and public affairs at Opinium said: “While the prime minister might have a world-beating new wardrobe, voters are refusing to wear his government’s austerity drive.

“Not only do the public feel worse off than they did before the election, but concerns that Labour has focused too much on government finances rather than growth have almost wiped out their lead on the economy. Much of the blame for this tone is being directed at Keir Starmer and Rachel Reeves, who now have approval ratings on a par with Rishi Sunak.”