Labour has lost Hartlepool, a constituency it had held since its creation in 1974.

So what went wrong and what does it mean?

– What happened in Hartlepool?

Conservative candidate Jill Mortimer has become the new MP, defeating Labour’s Paul Williams.

The importance of the contest was underlined by both Boris Johnson and Labour leader Sir Keir Starmer making repeated visits to the constituency during the course of the campaign.

– How bad a result is this for Labour?

Very. It is rare for a governing party to gain a seat at a by-election, the last one was another northern Labour seat in Copeland in 2017 and before that you have to go back to Mitcham and Morden in 1982.

In the event, the Conservatives overturned a 3,595 Labour majority at the 2019 general election to cruise home with a majority of 6,940 on a 16% swing.

Ms Mortimer took more than half the vote with 15,529 while Dr Williams trailed a distant second on 8,589.

In part, it was the result of voters switching from the Brexit Party, which took a quarter of the vote in 2019, to the Tories.

However, worryingly for Labour, the party saw its share of the vote fall by almost 9%, suggesting that replacing Jeremy Corbyn has not helped it regain the ground lost in its former heartlands.

– What has been the reaction?

On the Labour left, sidelined under Sir Keir, there were immediate calls for the party to change direction and return to the path set out by Mr Corbyn.

Diane Abbott said it was not possible to blame the former leader and called on Sir Keir to “think again about his strategy”.

The grassroots Momentum group said replacing “meaningful policy with empty buzzwords” had failed and without a change of direction, Labour could be permanently out of power.

However shadow communities secretary Steve Reed said while it was a “shattering” result for Labour, it was time to double down on Sir Keir’s centrist approach.

“We now have a leader that the country could see as an alternative prime minister – the problem is the Labour party itself,” he said.

– So what next?

Unless Sir Keir can hit upon a formula for winning back voters in northern England, then his chances of getting the keys to No 10 at the next general election appear remote.

But while the Labour leader has his critics, notably those on the left of the party loyal to Mr Corbyn, his position appears secure, with most MPs acknowledging the scale of the challenge he faces and the way in which the pandemic has meant his first year in office has been far from normal.

However, Westminster is rife with rumours that a shadow cabinet reshuffle could be used by Sir Keir to bring in fresh faces in an effort to revive the party’s fortunes.