Support for the Labour party jumped after Keir Starmer became leader 10 months ago but the progress in winning over British voters has stalled in recent weeks despite the error-strewn handling of the Covid-19 pandemic by Boris Johnson.

Much of the newfound support for the UK’s main opposition party has come from former supporters of the smaller Liberal Democrats and Green party, often in Labour-held seats, according to recent internal Labour polling.

But, worryingly for Sir Keir, it showed that the party had won over just 4 per cent of people who had voted Conservative when Mr Johnson, the UK prime minister, secured a resounding election victory in 2019.

This failure explains why the Labour leader has adopted a pro-family, patriotic message to try to win back working-class voters in the so-called “Red Wall” seats, former Labour strongholds that went Tory at the election. The approach mirrors Joe Biden’s successful strategy that helped him claw back blue-collar voters from Donald Trump in the US.

Following a string of positive headlines about the Tory government’s vaccine programme in recent weeks, Labour officials are starting to fret about their prospects for May’s local elections.

A strategy document drawn up by an external consultancy and leaked to The Guardian this week, advised Sir Keir to woo former voters by brandishing the Union flag, praising military veterans and dressing smartly — all of which he has been doing for months. It also warned that voters still believe Labour is the party of “spend, spend, spend”.

UK opinion poll,Voting intention of respondents (%)

Slides at the presentation featured focus groups’ comments such as “they [Labour] have been way too quiet”. Another called Labour “two different parties under one name”. The party has long straddled two demographic groups: urban white-collar left-wingers and blue-collar workers in the northern industrial heartlands.

In 2019, Mr Johnson peeled away many pro-Brexit working-class voters from Labour who did not trust Jeremy Corbyn, the party’s “hard left” leader at the time of the election.

The leaked document angered some leftwing MPs who accused Sir Keir of trying to ape the Conservatives.

By seeking to close down criticism of Labour’s lack of patriotism, Sir Keir is partially adopting the tactics used by former prime minister Tony Blair, the party’s most successful leader. “It is excellent news that the Labour party is finally listening to the voters after 10 years of not doing so,” said Ben Bradshaw, the Blairite Labour MP for Exeter.

Helen Goodman, former MP for Bishop Auckland, which turned Tory in 2019, said she thought the strategy was working. “It’s absolutely true that people won’t vote for a party they don’t trust with the country’s defence and I am now hearing people who voted Tory last time say they do trust Keir and will vote Labour again.”

After closing a gap of about 12 percentage points since Mr Starmer replaced Mr Corbyn as leader — the FT’s poll of polls had the two main parties neck and neck at Christmas — the Tories have since pulled ahead somewhat.

The majority of voters for all major parties approve of how the government is handling the rollout of the vaccine

One member of the shadow cabinet said Sir Keir had presided over the biggest increase in support enjoyed by any new Labour leader in modern history. But that extra support was piling up in urban seats that the party already controls, rather than in the Red Wall seats it needs to regain, she warned.

“If we had an election tomorrow then David Lammy [MP for the London seat of Tottenham] would get a majority of 100,000 or whatever, but that doesn’t help us in seats like Grimsby,” she said referring to one of the former Labour strongholds in north-east England.

Some MPs fear that Sir Keir, a London-based lawyer who backed Remain in the Brexit debate, has not gained traction in the traditional former Labour heartlands.

“There is a sense that momentum has slowed. He did well initially to close the gap but Labour is finding it harder and harder to cut through,” said Deborah Mattinson, a pollster and author of Beyond The Red Wall, a book on Labour’s northern struggles.

Labour had hoped to exploit the government’s failings on the pandemic, such as the haphazard procurement of PPE last year, and the economic fallout.

Instead, many voters still believe the government is “unlucky” rather than incompetent, and have been impressed by the recent vaccine progress, according to pollsters. Mr Johnson’s attempts to paint Labour as a carping bystander have also had some traction.

Marcus Roberts, director of international politics for YouGov, said Sir Keir needed to get the party, which is polling around 39 per cent, well past the 40 per cent threshold.

Poll asking Does Keir Starmer look like a prime minister in waiting?

“Midterm poll leads for the left are always reduced by voters on the day. If you want to win an election you can’t be eking out a tiny poll lead,” he said. Ed Miliband, the former leader, was 12 points ahead of the Tories in 2013 but still lost the 2015 election.

The internal polling suggests that the party could lose seats in May’s local elections in some “Red Wall” areas such as Bolsover and West Bromwich. The crucial mayoral elections in Teesside and the West Midlands, where Labour needs to topple Tory incumbents, also appear to be finely balanced.

A debate is brewing in the shadow cabinet over whether Labour needs to roll out new policies for the first time since the last election to engage with voters. Mr Miliband, now shadow business secretary, is among those wanting to flesh out the party’s prospectus, while shadow chancellor Anneliese Dodds is among those who are more cautious.

Natascha Engel, former MP for North East Derbyshire, said Sir Keir’s challenge cannot be solved by policies alone. “If Labour wants to represent Red Wall voters again the Labour party has got to like them, and we’re quite a long way off that,” she said. “There are no silver bullets that will make the voters we lost suddenly vote Labour again.”