“With all the wealth of evidence now, with all the sociological evidence, all the epidemiologists, all the educationists, the idea of going back to selection aged 11 is a bit like a health secretary saying I’m going to go back to applying leeches as a way of restoring health.”

Labour politician Alan Johnson, speaking to us ahead of his appearance at the Cambridge Literary Festival this weekend, is more than happy to share his opinions. Ranging from the state education system to the Labour Party’s current existential crisis, Johnson is unafraid to offend the big names in British politics.

We begin by discussing his latest memoir, The Long and Winding Road, which deals with his struggle to reconcile his working-class upbringing with the hallowed corridors of Westminster. As to the question of whether he still identifies as working class, Johnson is unequivocal.

“I didn’t go to university. I left school at 15. I lived in social housing until I was 39. I would say that the definition [of your class] is where you come from, and how you feel most comfortable, given that we do live in a very class-dominated society.”

In this regard, Johnson is a refreshing contrast to the Cameron–Osborne public school ‘chum-ocracy’, and even his former party leader Tony Blair. Despite this, Johnson makes clear that he is not into class war. He recounts a revealing anecdote to explain.

“When I was a postman, in those days loads of Christmas casuals used to come in”, he tells us. “When I was 18, there was a kind of mutual incomprehension. For us it was inconceivable that we went to university, and for many of the kids coming in it would have been inconceivable for them not to have gone to university, and there was a kind of feeling of being from different planets, but we got on well and it was fine and the post all got delivered.”

Perhaps it is this spirit of inclusiveness which drives Johnson to be so vocally against grammar schools’ segregation of people at such an early age. He laments “the psychological effect on the kids who failed at aged 11: they carried that burden of failure for the rest of their lives.”

“All those bright kids, much brighter than us some of them”, he muses, “but just on that one day, failed that one test, and were condemned to be second-class citizens as far as education was concerned.”

Johnson goes on to suggest that the plans for the reintroduction of grammar schools would contradict Theresa May’s early rhetoric. “It’s a ludicrous thing for her to suggest, and I think it’s done her some damage actually because I think if she really does believe in the very important words she said on the steps of Number 10 about social mobility, and all of that, then she wouldn’t go anywhere near this.”

Theresa May isn't the only prime minister to come under fire from Johnson. He has strong words for her predecessor and his decision to hold a referendum. “It was triggered because David Cameron wanted to solve a problem in the Conservative Party. It wasn’t a problem in the 2015 general election.”

“All the feedback from the Right and the Left showed that immigration was an issue, but not having a referendum on the European Union. That came well down people’s lists of priorities.”

Many have seen immigration as representative of the Labour Party’s current crisis. It could be argued that Labour faces an existential crisis, in that, while its MPs tend to be outward-looking and Europhile, its more traditional core supporters are generally less pro-immigration.

Johnson does not accept this completely. “On immigration, we’re with the vast majority of the British public, in that immigration has been good for this country, but the people who come in should learn the language, obey the law, and pay their taxes, and that immigration has to be controlled.

“I believe that free movement is a fair quid pro quo for the single market and the customs union, just like freedom within the United Kingdom works between the four nations of the United Kingdom because we’re one entity.”

However, Brexit changes this. “If we’re not in the European Union, then that’s the end of free movement, and I think we’ll lose a lot else.” How does he think we should proceed? “I don’t think it’s about hard Brexit or soft Brexit, it’s about sensible Brexit or stupid Brexit”.

He elaborates: “I wouldn’t be prepared to vote against leaving the European Union, but I would be willing to vote for amendments that gave the parliament some kind of control over this process”. And yet, he is not necessarily optimistic for our country’s future. “The idea that you just cut off everything," he tells us, "and everything would be alright because we’d have all these brilliant trade deals with other countries is bizarre and perverse, and I don’t think that’s what Theresa May believes.”

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When asked about John McDonnell’s recent claims that resisting Brexit would put Labour on the side of “certain corporate elites”, his response is clear. “It’s a ridiculous thing to say. I mean, there’s hundreds of thousands of trade unionists who worry not just about their jobs and their industry (the car industry, for instance) but also about workers’ rights.

“No one I’ve spoken to in the Labour Party is trying to overturn it,” he says of the referendum result. But he makes clear that “it didn’t determine how we came out”. He tells us: “we have to make sure we don’t damage the national interest, damage our economy, damage jobs, and damage our future.”

He good-naturedly agrees that Labour as yet have not set out a clear idea of how this could work. “It’s a fair criticism of us, as our Majesty’s official opposition, to say ‘you’re telling the government they have to set out a plan, perhaps you ought to let us into a few of yours as well’. We have to have a more sophisticated idea of where we’re going on this.”