Now is “not the time” for Labour to go through another leadership contest, deputy leader Tom Watson has warned.
He told BBC One’s Andrew Marr Show that despite lagging substantially behind Theresa May in opinion polls, Jeremy Corbyn was “established” in the role.
Mr Watson also downplayed suggestions Labour was testing the popularity of alternative candidates for leader.
He said the party faced an “uphill struggle” to win the next election and had to offer “positive” ideas.
Mr Corbyn was first elected Labour leader in 2015 and won again last year in another contest.
Mr Watson said the party had “got the leadership settled for this Parliament”.
The most recent ICM opinion poll put Labour on 27%, 15 points behind the Conservatives. And a YouGov poll suggested that 62% of voters were unfavourable towards Mr Corbyn, compared with 22% who were favourable.
The Sunday Times is reporting that Labour is involved in “succession planning”, and research carried out on its behalf suggests Mr Corbyn is the “most unpopular” choice.
But Mr Watson told the Andrew Marr Show: “I only saw this story last night. People tell me that isn’t the case, it wasn’t road-testing leadership candidates.
“There was a range of shadow cabinet members that were so-called road-tested, this is what we do in our normal run of political consultations.
“I’m just slightly relieved they weren’t road testing me on the document that was leaked to the newspaper.”
The churn in Corbyn’s shadow cabinet
Mr Corbyn saw off a challenge from Owen Smith last year, winning 61.8% of the vote – a higher share than in the first contest.
Mr Watson said: “This is not the time for a leadership election. He got a second mandate from our members last year. He is now the established leader of the Labour Party.
“It is his duty to lead the official Opposition through a period of unprecedented economic uncertainty and he will be tested. He has to explain those and he has to improve on them and he’s well aware of that.”
Last week, Mr Corbyn imposed a three-line whip – the strongest possible sanction – on his MPs to support the government’s Brexit bill, arguing that this reflected the will of the people, as expressed in last year’s EU referendum.
Shadow business secretary Clive Lewis resigned from the front bench, saying that to back the bill would go against his conscience. Altogether, 52 Labour MPs voted against Mr Corbyn’s orders.
Mr Watson said: “We’ve had a tough 18 months. We had a damaging second leadership election, so we’ve got an uphill struggle ahead.
“The polls aren’t great for us, but I’m determined that we’ve got the leadership settled for this Parliament, that we can focus on developing a very positive, clear message to the British people in a general election.”
He added: “We need to make sure we address the concerns of the British people in a manifesto and that we communicate our message far more clearly than we have been doing. But there’s nothing to say that Labour can’t win a general election.”
Mr Watson said Labour had to convince voters the party wanted “this country to be great again, that if you live and work hard in this country you can eventually own your own home or rent a home at an affordable price, have a job that is satisfying and then have a dignified retirement.
“Political parties that don’t address those issues are political parties that don’t have a future.”
He described Labour as “a patriotic party”, saying: “We’re very proud of our country and very proud of singing the national anthem.”
ICM interviewed 1,984 adults from 3 to 5 February. For its poll, YouGov interviewed 1,670 adults on 2 and 3 February.