Labour leader Keir Starmer said the party deserved to lose the last UK election as he urged colleagues to “get serious about winning” — in a merciless repudiation of the Jeremy Corbyn era.

In his first party leader’s conference speech since taking over from Mr Corbyn in April, Sir Keir said it was pointless for a political party to be in opposition. He also launched a withering attack on prime minister Boris Johnson saying he was not “up to the job”.

“The promise that brought us all into politics, to change the country for the better, is pointless if all we can do is object to endless Tory governments,” he said, in an address to members via video link.

Sir Keir said he was frustrated that all of his front bench MPs were still shadow ministers rather than actual ministers in a government. “When you win you come out of the shadows,” he told them.

Labour lost 59 seats during the general election in December — its worst result in almost a century — under Mr Corbyn, a veteran of the “hard left”. “Let’s be brutally honest with ourselves. When you lose an election in a democracy, you deserve to,” said Sir Keir.

“You don’t look at the electorate and ask them: ‘What were you thinking?’ You look at yourself and ask: ‘What were we doing?’”

Recent polling has suggested that Labour has largely closed the gap with Mr Johnson’s ruling Conservative party while Sir Keir is seen by voters as a credible leader.

Yet the party faces deep structural problems including the loss of working-class pro-Brexit voters in England and the collapse of its support in Scotland since the 2014 Scottish independence referendum. Labour only has one MP in Scotland, down from 41 in 2015.

The current Labour leadership blames its losses in the so-called “red wall” — constituencies in the north of England and Midlands which have traditionally voted for the party — on a mix of the party’s anti-Brexit position, animosity towards Mr Corbyn and a lack of economic credibility.

Speaking from Doncaster, a northern English town where Labour clung on to two seats in December — albeit with much smaller majorities — the leader urged former supporters to “take another look” at the party.

“We’re not going to win back those we’ve lost with a single speech or a clever policy offer. Trust takes time,” he said. “It starts with being a credible opposition.”

Labour has so far offered no new policies this week, mindful that the next general election is more than four years away.

When the Covid-19 pandemic struck in the spring Sir Keir eschewed knee-jerk criticism of the government in favour of constructive criticism. In Tuesday’s speech, however, he launched an acute critique of Mr Johnson, saying he was “not serious”.

If the UK entered a second nationwide lockdown, it would be a sign of government failure rather than an “act of God”, he said, accusing ministers of having lost control — for example with the failures in the Covid-19 testing system.

The prime minister had wished problems away — from coronavirus to Brexit — rather than tackling them sensibly, he argued. “It makes me angry that just when the country needs leadership we get serial incompetence.”

Sir Keir contrasted his career as a defence barrister and former director of public prosecutions with Mr Johnson’s past as a newspaper columnist. “While Boris Johnson was writing flippant columns about bendy bananas, I was defending victims and prosecuting terrorists,” he said. “While he was being sacked by a newspaper for making up quotes, I was fighting for justice and the rule of law.”

Sir Keir reminded listeners that he had received his knighthood at Buckingham Palace for services to criminal justice.

During the speech, Sir Keir did not mention Mr Corbyn once by name, and instead referenced Tony Blair — who won three elections as Labour leader but is hated by many leftwing members.

Andrew Scattergood, co-chair of Momentum — the leftwing activist group that was key to Mr Corbyn’s rise — said Sir Keir’s speech was a “missed opportunity to show substance”. He called on the leader to make good on his promises from his leadership campaign to tax the super-rich and corporations.

But Paddy Lillis, general secretary of the Usdaw retail union, praised the speech: “He is delivering a competent and credible opposition that knows Labour needs to win in order to change people’s lives, and our country, for the better.”