Labour leader Sir Keir Starmer has insisted the party is “fighting for every vote” in the Hartlepool by-election as an opinion poll showed the Tories opening up a double-digit lead in the constituency.

Ahead of Thursday’s vote, the Survation poll for ITV’s Good Morning Britain put the Conservatives on 50% – 17 points ahead of Labour in a seat it has held since it was created in 1974.

Sir Keir, who has visited the constituency three times in the course of the by-election, said he hopes Labour will not lose another seat in the party’s so-called “red wall”.

However he acknowledged that the party still has a “mountain to climb” after the devastating defeat under Jeremy Corbyn in the 2019 general election if it is to get back to a position where it can regain power.

“I hope we won’t lose Hartlepool. We are fighting for every vote there. I know that every vote has to be earned,” Sir Keir told BBC Radio 4’s Today programme.

“I said on the day that I was elected (Labour leader) that it was a mountain to climb. It is, we are climbing it and I’ve got a burning desire to build a better future for our country.

“I don’t think anybody realistically thought that it was possible to turn the Labour Party round from the worst general election result since 1935 to a position to win the next general election within a period of one year.

“It was always going to take longer than that.”

International Trade Secretary Liz Truss said that despite Labour’s difficulties, it was still a “massive challenge” for the Conservatives to take the seat.

“I think the fact that Labour is facing such difficult circumstances in their heartlands goes to the issue of what the problem with the the Labour Party is, which is they’ve lost sight of standing up for working people, of standing up for jobs and growth in Britain, and that’s what we’re campaigning on,” she told Times Radio.

“We’re running a positive campaign, but it would be a hard task to win a seat like Hartlepool which really has been Labour for generations.”

With voting taking place across Great Britain on Thursday – including for English councils, the Scottish Parliament and the Welsh Senedd – Sir Keir acknowledged he is facing his first major electoral test.

“I take full responsibility for the results, just as I take full responsibility for everything that happens in the Labour Party under my leadership,” he said.

Since the turn of the year, the polls nationally have consistently shown the Conservatives ahead – although there was some tightening over the weekend, suggesting the charges of “sleaze” may be beginning to cut through.

Sir Keir expressed exasperation that lockdown rules had restricted his ability to get out and campaign in the year since he became leader.

“I have been beyond frustrated. I haven’t addressed a roomful of people as leader of the Labour Party. Every single speech has been in a sterile room down the barrel of a camera,” he said.

“Forget kissing babies, I’ve not been able to shake the hand of a single voter. So am I frustrated? Of course I am.

“I am pleased now that, at last, I am getting the chance to get out there and show who I am and what I stand for and what I want to do and what my burning desire is to change our country for the better.”

The inequality that’s built into our economic model is morally unjust, but it’s economically stupid

Sir Keir, who has faced criticism for his failure to make more of an impact in the polls since the successful rollout of the vaccination programme, insisted he had been right to pursue a policy of “constructive opposition” during the pandemic.

He said that, as the country emerges from the pandemic, Labour is committed to tackling the “inequality and injustice” of the Tory years.

“The inequality that’s built into our economic model is morally unjust, but it’s economically stupid,” he said.

“The inequality and injustice in our economy were baked in because of austerity before we got to the pandemic and, as we come out of the pandemic, we’re at a fork in the road.

“We’ve got to decide, do we go on to a different and better future, or do we go back and try to patch up what we had before?”

– Survation interviewed 517 Hartlepool residents aged 18 and over by telephone between April 23 and 29.