The UK's relationship with the EU looks set to become an issue in both a possible Labour leadership contest and the coming by-election in the Makerfield constituency.
Former Health Secretary Wes Streeting, in his first public appearance since resigning from the cabinet, told an audience in London on Saturday that "leaving the European Union was a catastrophic mistake".
At the Progress Conference, organised by the "Blairite" wing of the Labour Party, he announced he would contest a formal challenge to replace Sir Keir Starmer.
Within an hour Conservative Party Chairman Kevin Hollinrake seized on Streeting's comment, saying "whilst Labour relitigate Brexit, Britain is not being governed".
Hollinrake called the remarks "yet another distraction... at a time when families and businesses want the government focused on the cost of living, the economy, public services and Britain's defence".
Under Sir Keir Starmer, Labour have trod warily around the issue of Brexit, sticking to "red lines" that, while seeking a closer relationship with the EU, the UK would not be rejoining either the EU's single market or a customs union.
In his speech, Streeting said Labour had suffered from an "overcautiousness" when formulating policies in opposition. He said the party had been "too afraid of what the Tories might say" but must now deal with "the big issues that define our age".
He listed "three big, important choices we have to make as a country".
First on his list was Brexit.
"It has left us less wealthy, less powerful, and less in control than at any point since before the Industrial Revolution," Streeting said.
"The biggest economic opportunity we have is on our doorstep. We need a new special relationship with the EU, because Britain's future lies with Europe – and one day back in the European Union," he added.
He made clear this could only happen if a new mandate was secured, such as at a general election.
Streeting's comments have put Andy Burnham's position on the issue under the spotlight.
On Saturday the Greater Manchester mayor was out canvassing for votes in the Makerfield constituency. He hopes to be the Labour candidate in the coming by-election, which the BBC understands will likely take place on 18 June. If he wins he'd be able to challenge for Labour's leadership.
He was asked by ITV News whether he was in favour of rejoining the EU and said "in the long-term there is a case for that". But he said he is "not advocating that in this by-election".
In the past Burnham has, like Streeting, said he respects the expressed will of the British people on Brexit and any move to rejoin the EU could only come if a fresh mandate had been secured.
Reform UK is hoping to use the issue to galvanise voters in Makerfield.
It said that 65% of people in the area voted for Brexit in the referendum in 2016.
There are no precise figures for how the party performed in Makerfield during the local elections because the ward boundaries do not fully align with the constituency boundaries.
But roughly, Reform pulled in 50% of the vote share, with Labour at 27%, the Greens at 10%, Conservatives at 7% and Lib Dems at 4%.
The party pointed to remarks Burnham made at Labour's annual conference last year where he said: "I hope in my lifetime I see this country rejoin the European Union."
A Reform UK spokesperson said Burnham "will not want to remind voters of those comments, but we will do it for him".
On the focus of his by-election campaign, Burnham told the BBC: "Britain has been on the wrong path for 40 years."
"It started in this borough with de-industrialisation, de-regulation of the buses, privatisation of life's essentials," he said.
He added that "we need a new path, we need to fix politics, to fix the economy, get the basics back under public control".
He said he wanted to see "re-industrialisation" of northwest England and a council house building programme "on a similar scale to the post-war period".
But the fact the UK's relationship with the EU has been seized on already by Streeting – as well as by the Conservative Party and Reform UK – is a sign of how the issue remains a key dividing line between political parties and voters.
The Liberal Democrats have already said that the results in recent elections have strengthened their long-standing argument that the UK needs change, insisting that "without a customs union, we won't see the growth we desperately need, and the forces of populism on both left and right will only grow".
Speaking for the Green Party at its conference last year, MP Ellie Chowns said "full membership of the EU remains the best option for the UK, and we are in favour of pursuing a policy to re-join as soon as the political will is present".
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