Chris Mullin is a bit of a mystery. A leftwing troublemaker who managed to serve in the Blair government; a weedy-looking operator who took on the police and the IRA to free the Birmingham Six; an idealistic socialist reporter who freelanced for the Sun and Telegraph; a dedicated parliamentarian who did not enter the Commons until he was 39; a writer of conspiratorial novels who reinvented himself as a self-deprecating, almost cosy political diarist – Mullin, now 68, has folded together multiple careers more like a Victorian than a modern MP.

Hinterland is another canny, deceptively casual Mullin performance. Covering his whole life, including phases already covered by his highly successful diaries, this slim book begins as a series of loosely connected anecdotes, after-dinner in tone, apparently random in their chronology, about the Labour party in the 70s and 80s. Mullin describes a boisterous, off-duty union leader, Norman Willis, a “long-winded” Neil Kinnock, and Tony Benn’s tumultuous 1981 challenge for the Labour deputy leadership. It’s all vivid stuff; but anyone who knows the party’s history will be familiar with most of it already.

Yet within a few pages you begin to realise that Mullin’s conversational but cutting little stories have contemporary resonances. A Benn ally who is falsely accused by the Labour right of organising intimidatory heckling at party meetings turns out to be Jon Lansman, now one of Jeremy Corbyn’s lieutenants, and founder of the leftwing pressure group Momentum, often unfairly accused of behaving in exactly the same bullying way.

A similar reality check for demonisers of the Labour left comes with Mullin’s account of how he captured his constituency, Sunderland South. In 1987 it was a longstanding Labour seat with a shrinking majority and a right-leaning MP, Gordon Bagier, best known for his support of the Greek military junta and about to enter retirement. To succeed him, Mullin had to outmanoeuvre an “oligarchy” of trade union and Labour rightwingers, who were used to manipulating the local party by “flooding” it with temporary members – again, precisely what the Labour left is currently being condemned for doing.

Mullin held the seat for 23 years, despite the disintegration of the local shipbuilding and mining industries that had previously been the source of much of Labour’s support. He refers to Sunderland as “the Deep North”, and still lives a few dozen miles away, he tells us in a rare moment of ostentation, in a cottage with a lawn which “takes three hours to cut”.

He was born in a different world: the postwar suburbs of Chelmsford, in Essex, where both his parents worked for the telecommunications company Marconi. They were relatively prosperous and upwardly mobile, and sent him to a private boarding school. “I was bullied mercilessly,” Mullin writes, “but I knew I would outlive the bullies … [as] one of only a handful of the students to make it into the sixth form and from there to university.”

Usefully for his later battles with the establishment, Mullin studied law. He doesn’t explain how he became political – sometimes this book’s omissions feel as significant as its confessions – but he does admit that a summer job at Pontins was “my first encounter with the working classes”, and that he found them “cheerful, decent people”. In 1970, at the precocious age of 22, he was selected as a Labour parliamentary candidate in North Devon. He lost his deposit.

For the next decade and a half, he restlessly explored the large territory which existed in the 70s and 80s for confident young Britons who were interested in both leftwing activism and journalistic adventures. He nosed around wartime Cambodia, Laos and Vietnam. Occasionally he got a scoop, such as his discovery that the Daily Telegraph correspondent in Vietnam “whose reports appeared under the byline John Draw was … Nguyen Ngoc Phach, an officer in the army of the southern regime”. When Mullin got back to Britain, following the more leisurely rhythms of journalism then, he “offered the information … to the editor of the Guardian diary column”. The editor “declined to use it on the grounds that it was ‘a bit so-whattish’.”

His relationship with his wife in postwar Vietnam is recalled with a melodrama that could almost be Graham Greene

South-east Asia changed Mullin. There, he learned that there was often “something wrong with the official version of events”. He acquired a suspicion of America, which runs caustically through the rest of the book, and which set him apart from the unthinkingly transatlantic politicians who would come to dominate Labour during the Blair era. And he met his Vietnamese wife, Nguyen Thi Ngoc. The perilous early stages of their relationship in authoritarian postwar Vietnam are recalled with a tenderness and melodrama that could almost be Graham Greene.

Elsewhere in the book, the quietly, carefully spoken Mullin rations the emotional moments. “I was a lonely youth with an overwhelming sense of social inferiority,” we suddenly learn on page 63. In the penultimate chapter, he abruptly admits to “fragile self-esteem”, even as a government minister. In a passage that anyone who thinks politicians are an impregnably self-assured elite could usefully read, Mullin writes about dragging a wheelie suitcase to his basement flat in south London after each red-carpet trip abroad as a Foreign Office minister, and feeling “as though I had been on the set of a film for the previous few days”.

Mullin made the transition from being a major source of irritation to the Labour hierarchy – in the early 80s, he published a still-infamous guide for rebellious party members, How to Select or Reselect Your MP – to being a minor Blair favourite because his views were more eclectic and pragmatic than those of most leftwingers. His decades in Sunderland left him sceptical about union power and liberal approaches to crime. His encounters with an over-mighty state in Vietnam made him sympathetic to some of New Labour’s privatisations.

But it would be a mistake to imagine he abandoned all his radical convictions. When I interviewed him last year about Whitehall’s barely disguised horror at the possibility, however remote, of Jeremy Corbyn becoming prime minister, Mullin was as keen as ever to rehearse the argument of his 1982 novel A Very British Coup: that any truly leftwing government would be illicitly destabilised by what he calls here the “unseen hand” of the British establishment. It’s a typical Mullin phrase: understated, streetwise, slightly mocking of the powers-that-be.

This book is a little too brief, and too bulked out with recycled material and plugs for other volumes, to be a classic political memoir. But it is an unusual and sometimes inspiring one, written by an unusually fearless politician. Halfway through, Mullin quotes an editorial he wrote for Tribune, the once-influential leftwing Labour journal which he edited with typical mischief and prickliness from 1982 to 1984: “This paper is not the property of any sect, tendency or personality … ” The same could be said of him. With luck, Labour’s current leftwing phase will produce a new Mullin or two before it is snuffed out.

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