For the first time since the UK left the EU, we have a prime minister who will "unflinchingly" debate Brexit, says the BBC's political editor Chris Mason.

By Chris Mason The Brexit debate is back. For years, it felt like the only thing Westminster talked about.

I have had a ringside seat at it all, from the Conservative election victory in 2015, with the party's promise in its manifesto that year to offer "a straight in-out referendum on our membership of the European Union by the end of 2017." Then there was the then Prime Minister David Cameron's negotiation with the European Union to try to secure what he saw as a better deal and then the referendum itself on Thursday, 23 June 2016.

And that, you will remember, was merely the start, as years of wrangling began. Two general elections came and went in 2017 and 2019 and it took the two prime ministers after David Cameron, first Theresa May and then Boris Johnson, before the UK left the European Union at 23:00 on Friday, 31 January 2020.

Little wonder perhaps that by that point, almost irrespective of someone's views on the topic, there was an appetite to talk about something else. Anything else. Political parties picked up that vibe and while their long standing instincts on the EU were there to see if you scratched the surface, there was minimal desire to extemporise about them any time soon.

With the arrival of Andy Burnham as prime minister, that has changed, despite what he said just a few months before he arrived in Downing Street.

He has been happy to repeatedly lean into an argument claiming that it is time to "face up to the reality that Brexit has done more harm than good" and "the status quo is not good enough for Britain." First he made this case at the Labour Party Conference last month and now he has made it again in the House of Commons. Burnham is attempting to make a two-pronged case.

First, in the short term, he wants to "deepen" the UK's relationship with the EU at a summit in Brussels at the end of next month. He insists such a deepening would be within the promise made by Labour at the last general election that the UK would say no to the customs union, the single market and freedom of movement.

Which brings us onto the second element of his case, in the medium term. What might Labour promise in its next general election manifesto? The prime minister told me a fortnight ago the manifesto could promise an in-out referendum. In the Commons, he sought to reassure you, whatever your view on Brexit.

"This country in the next decade needs to know where it's going. There are no assumptions here, and as I said, the British public will be the boss of whatever is decided," he said. Hang on, say critics, it was decided by voters a decade ago.

"They weighed the arguments and made a decision. The least they are owed is politicians willing to defend it," argues Lord Frost, a former Brexit minister and chief Brexit negotiator in the Telegraph.

The focus of the next five weeks, ahead of a UK-EU Summit in Brussels on Friday 20 November, is what Downing Street sees as short term wins on youth mobility, food and drink, and energy.

Andy Burnham hopes to make an argument that what he will portray as a sensible, pragmatic deepening of the relationship with Brussels can help cut illegal immigration and boost economic growth.

He sought to goad the Conservative leader Kemi Badenoch for seeking to oppose a plan he thinks can contribute to growth. She argued it risked regurgitating yesterday's arguments with little prospect of success.

And, strikingly, his attempt at goading his opponents went further still. He told The Rest Is Politics podcast that upon arriving in Downing Street, he had asked if there was Russian interference in the Brexit referendum.

"I've had a clear answer that, yes, there was," he claimed, without saying who provided that clear answer or what the evidence for that suggested clarity was.

In the Commons, his language appeared a little softer. He told MPs it was "inconceivable" to think that Russia did not try to interfere. A double negative deployed this time, about alleged attempts at interference.

His political opponents were already pouncing. The Reform UK leader Nigel Farage was blunt – calling the prime minister "a liar." The former Prime Minister Boris Johnson added that he had asked the same question as Andy Burnham did when he became Foreign Secretary "and they replied that there was no evidence of any successful interference in the 2016 referendum, by Russia or any other power". And so a debate resumes about the difference between attempted interference, interference and successful interference.

But the key point is this: for the first time since the UK left the European Union, we now have a prime minister who is willing to unflinchingly debate Brexit: whether it is working, how it is working, how to improve it, and if it's proved to be a failure.

In so doing he hopes he can tap into public sentiment which opinion polls suggest a perception among a majority that leaving the European Union hasn't turned out how many might have hoped.

On top of this, he hopes to lure pro Europeans broadly on the Left who may recently have supported the Liberal Democrats, the Green parties of both England and Wales and Scotland, the Scottish National Party and Plaid Cymru towards Labour. That is the political logic from the government's point of view, for now at least.

And as for where all of this leads – well, good question. In the coming weeks, months and perhaps years, there may be a Back to the Future vibe to our political debate. A splash of familiarity, as a conversation about the relationship we have with our nearest neighbours resumes.