The first anniversary of Keir Starmer taking the reins of the Labour party comes at a very awkward moment considering his standing in the polls.

His approval ratings have tanked from record highs to his first negative ratings in the last few weeks. Last June, Ipsos Mori found Starmer enjoyed a rating of +31%, the joint highest for any leader of opposition since the polling company began tracking opposition leaders in the 1970s.

Starmer’s standing slipped to a still respectable score of +15% in October. But by March, only 33% were satisfied with the job Starmer was doing, compared with 42% who were dissatisfied, giving him a net score of -9%. Britain Elects also put Starmer in negative territory for the first time in March.

“He’s got to turn that round,” says Keiran Pedley, the director of politics at Ipsos Mori.

One of the most worrying aspects for Starmer was his rating among Labour supporters, Pedley said. “What has stood out for me is one in five Labour voters from 2019 say they are unfavourable towards Starmer and one in five think he is going to move the party in the wrong direction. They don’t think he is opposing the government strongly enough.”

This could be the start of a “José Mourinho factor” for Starmer, Pedley said. Like the football manager, Starmer managed to persuade Labour supporters that he was a winner, even if they had doubts about his tactics. But when Mourinho’s teams start losing, fans are very quick to lose heart. So if Labour were to do badly in next month’s local elections and the byelection in Hartlepool, party supporters and MPs could really turn on Starmer, Pedley said.

“I’d be surprised if he faced a leadership challenge, because the threshold for that is high, but if they lost Hartlepool, that could be quite a big symbol,” he added.

James Johnson, a former Downing Street pollster who worked under Theresa May, found that voters were unsure about Starmer. His firm, JL Partners, found 37% agreed the reason they would not vote Labour was that it was unclear what Starmer stood for.

Pedley has noticed a similar trend. He said: “People say they don’t know enough about him, and there may be a sense he sits on the fence. It is fair to say there is no obvious Starmerism.”

But this is not necessarily harmful to Starmer. Pedley pointed out that people knew what Corbyn stood for and he suffered record lows in approval ratings. “Even now Starmer’s ratings are better than Corbyn was getting.”

So while the polling shows the “honeymoon is over” for Starmer, it is too early to write him off, according to Pedley.

The success of the vaccine programme makes this a particularly challenging time for a leader of the opposition. Even 85% of Labour voters are satisfied with the vaccine programme, according to Ipsos Mori. Pedley said: “The external environment Starmer is operating under is quite unique and likely to change – governments don’t have positive headlines for ever, so maybe this is just a blip.”

Starmer could draw comfort from the example of David Cameron. A year after being elected Tory leader, Cameron had an approval rating of -5%, but became prime minister four years later. Pedley said: “A year in, and it is clear that Starmer has got challenges, and you can’t just dismiss these because of the success of the vaccine programme.

“But the future is still very much up for grabs. We don’t know what the mood music around the government is going to be six months from now, never mind two or three years.”