Oh dear. I should like this. Everyone else does. The reviews say it is brilliant.
And it is indeed well-written, meticulously researched and an extraordinary piece of work.
But if I am honest I was bored. Sorry, but I was!
It depends partly on whether you can cope with history written in this sort of way:
"In 1937 James was posted to Budapest, a hotbed of international spy intrigue, where the British secret service operated a branch headed up by Lt.Col Wilfred "Squidgy" Sponge-Clibbon, who had been at school with James' father at Eton in the late 19th century when thrashings were commonplace under the headship of the notorious Major General Adolf Winterton-Snow. "Squidgy" was a spy of the old school, who drank six gins before breakfast and then spent the rest of the day asleep. But James was one of a new, eager breed of "telephonic" spies who knew how to make a phone call and were determined to use the new technology to their advantage. James was entranced by Budapest, not least by Fraulein Zsa Zsa Kratchupek's "Hot Lips" bar where all the spies would regularly meet to sell secrets over roulette. Ms Kratchupek was a colourful figure who had once drunk the Mata Hari under the table and smoked three-foot long cigars while serving drinks including exploding cocktails at the bar..."
Although admittedly it is possible my paraphrase is a tad unfair.
If you like that kind of thing, you'll love it.

Extremely readable, like a good novel. The British upper class ease their way through life and Old Etonians still seem to run everything (Cameron, Boris Johnson etc). It was the same in the 1930s when Kim Philby was everyone's friend, from the same class, with the same manners, but happy to betray them all.

Kim Philby ranks as one of the greatest spies in history, and one of the greatest traitors. Outwardly a charming member of the British establishment and MI-6, privately Philby was a committed Communist and passed every secret he could garner on to Moscow. One of the brightest of the Young Turks, Philby was being groomed for the top slot at MI-6.

Macintyre's book is a story of the friendship between Philby and his greatest defender, Nicholas Elliott, and of a whole British ruling class of the right sort of people: good families, public schools, Oxbridge, government service, and so on. Macintyre quotes C.S. Lewis on the role of the toxic idea of the Inner Circle on British society, that there are ever more exclusive clubs where real power is held, and this inner circleness drove and destroyed Philby, as much as any ideological commitment. After all, spycraft is more exclusive than ordinary government service, and being a double agent is more exclusive than being a spy.

Philby worked as a journalist through the 30s, concealing his true politics and getting close to Franco and prominent Nazis. He was a war correspondent during the Battle of France, and after the fall of France was posted into British intelligence as an expert in propaganda. He befriended Elliott, a true member of the elite (Elliot's father was headmaster at Eton), and began a meteoric rise through the ranks, turning over what he uncovered to his Soviet masters. Philby likely blew the defections of the Volkovs in Istanbul, turned over the names of hundreds of Catholic anti-Nazi and anti-Communist activists in Soviet occupied Germany, and doomed Albanian sabotage missions after the war. He has a lot of blood on his hands.

Philby was posted to America, where he befriended the anglophile James Angleton, the CIA counter-intelligence chief. Well-lubricated parties served him well, until his involvement with Guy Burgess, a more flamboyant and self-destructive Soviet spy in the British foreign office, derailed his career. Burgess was drunk, homosexual, loud, possibly brain damaged, and Philby's close friend and house-guest. When another of the Cambridge Five, Donald Maclean, was under immanent threat of being blown, Burgess was used to organize the escape. Philby fell under an immediate cloud, and while there was plenty of circumstantial evidence that he was also a spy, the Establishment protected its own, and while his career was iced, he remained free.

By 1955, a destitute Philby was back in good enough graces to be offered another intelligence job as an agent in Beirut. His marriage to Aileen Philby had by that point more or less disintegrated under the weight of deception, alcohol, and her mental illness. Philby spent another 8 years in Beirut, drinking heavily and a lackluster reporter (his cover) and agent. According to Macintyre, it was Philby's journalism that did him in. His pro-Arab slant annoyed an old acquaintance, the British Zionist activist Flora Solomon. Solomon had introduced Kim and Ailene, and remembered in the 30s that Kim had made a clumsy effort to recruit her as a Soviet spy. She had the credibility which MI-5 investigators lacked, and Elliott confronted Philby in Beirut, where Philby confessed. But then, incredibly, Philby managed to defect to Moscow, where he lived until dying in 1988. Macintyre convincingly argues this was deliberate, that the public spectacle of another spy trial in London would have so thoroughly discredited MI-6 that defection was a better option, and that a lack of surveillance was deliberately arranged.

This is a thrilling true story of a vanished age, when government was run by "gentlemen", and when being the right sort of person could forgive almost any transgression. The incestuous world of British intelligence is perhaps best revealed by a security briefing between Elliot and another officer.

[paraphrased]
OFFICER: Does your wife know what you do?
ELLIOT: I should think so. She was my secretary for two years first.
OFFICER: How about your mother?
ELLIOT: She does, a member of the War Cabinet told her I was a spy at a party.
OFFICER: And your father, does he know?
ELLIOT: Yes. The Chief told his at White's Club.

With the right accent, the right clothes, the right attitude, it was so impossible that Philby was a double agent that everyone ignored the evidence until it was far too late.

Fascinating and amazing tale of real life espionage.

A Spy Among Friends is the incredible story of Kim Philby, Englishman and Soviet double agent, who passed British and American secrets to Moscow for decades. The extent that Philby reported classified information was unbelievable. He had no qualms about sharing secret information that his friends and fellow intelligence officers told him in confidence to the USSR. I found myself holding my breath every time the author started to outline missions that were set up by the British because I knew that, thanks to Philby, they were going to fail. The book reads like a novel but at the same time you can't dismiss any of it as fantasy because it all happened.

Very good page-turner about the real-life inspiration for Tinker, Tailor, Soldier, Spy. Been on a bit of a spy kick, so this was a nice read.

I think listening to the audiobook counts as "reading" it. Fascinating.