Mal Evans began the 1960s as a Post Office engineer in Liverpool. By the end of the decade, he'd appeared in three out of five Beatles films and was an occasional musician on their albums. It was Mal playing the organ on Rubber Soul, Mal who sounded the alarm clock in A Day in the Life. On Abbey Road, it was Mal, not Maxwell, who banged the Silver Hammer.

Part of the Beatles' small but exceptionally protective inner sanctum, Mal was one of just two witnesses at Paul McCartney's first wedding. Among the hundreds of claimants to that threadbare title "fifth Beatle", he was arguably the most deserving. Wherever the Beatles went, Mal would never be far behind.

In the 10 years he spent as their road manager, Mal was blessed with a greater insight than most into the group's spectacular rise, their domination of pop in the middle years, and their painful implosion in a welter of recriminations. Throughout the decade, he kept a series of diaries and wrote an unpublished autobiography; all of this has until now remained unseen, part of an archive that went missing when Mal himself died in bizarre circumstances in 1976.

For many years, an ever-growing number of Beatles historians have regarded the Mal Evans archive as the holy grail. Last year, rumours surfaced that it had turned up in a suitcase in a Sydney street market (not true) and that it contained outtakes of unreleased Beatles songs (ditto). The reality is rather more prosaic: 10 years after Mal's death, Yoko Ono was told about a trunk full of his effects that had been found by a temp clearing out files in the basement of a New York publisher; she arranged for them to be shipped back to his family in London. Among those effects were the diaries, which his widow, Lily, kept for years in an attic at her home.

Together with some photographs, most of them taken by Mal himself, they amount to a fascinating collection: the unwitting historic recollections of a Forrest Gump of a man, who by sheer good fortune ended up in the right place at the right time.

The story, inevitably, begins in Liverpool. A keen rock'n'roll fan, Mal would while away what he called his "extended lunchtimes" at the Cavern Club before putting in a brief appearance at the Post Office and then heading off to his house in Hillside Road, Mossley Hill.

In 1961 he had married a local girl, Lily, whom he had met at the funfair at New Brighton. Their first child, Gary, was born in the same year. Mal's life was settled, mundane and ordinary; nobody could have predicted that the bizarre twists and turns of his life in the next 15 years would lead to a premature and avoidable death at the hands of the police in California.

At the Cavern, Mal was soon noticed by the Beatles, who had a lunchtime residency at the club. George Harrison felt that Mal, at 6ft 3in, would make an ideal bouncer. He was also of an exceptionally gentle disposition, and Harrison was canny enough to realise that this too would be useful in the years ahead.

In the first few pages of his 1963 Post Office Engineering Union-issue diary, which includes information about Ohm's law and Post Office pay rates, he reflects upon his good fortune. Looking back on the previous year, he writes: "1962 a wonderful year... Could I wish for more beautiful wife, Gary, house, car... guess I was born with a silver canteen of cutlery in my mouth. Wanted a part time job for long time — now bouncing... Lost a tooth in 1962."

With this, Mal sets the tone. We soon find he is more Pooter than Pepys. As the Beatles' road manager — and trusted implicitly by all four — he is presented with an "access all areas" ticket to one of the best parties of the century. Yet somehow he never quite realises it.

The year 1963 is crucial for the Beatles, ergo for Mal. At the start of the year it is becoming clear that working with them, particularly on tour, is a more engaging diversion for him than family life in Mossley Hill. The band, now managed by Brian Epstein, are beginning to realise their potential. Mal drives them to London for one of their early BBC appearances, and later they make the most of the capital.

January 21, 1963: "Lads went shopping. Paul and George bought slacks. George a shirt in Regent St. This was before the Sat Club recording and we lost them for a while. Back to Lower Regent Studios for recording talent spot. Met Patsy Ann Noble, Rog Whittaker, Gary Marshall, a really good show. Also on the bill was a Birkenhead singer. At about 8.15 the boys went to Brians room in the Mayfair for a Daily Mail interview. I parked the gear and joined them later... We left London at about 10 o'clock, stopping at 'Fortes' on M1 for large dinner — bought by the Beatles — and so homeward bound. Met a lot of fog... suddenly after leaving M1 short time windscreen cracked with a terrible bang. Had to break hole in windscreen to see... Stopped for tea at transport cafe... and arrived home at about five o'clock. I was up at 7.45 but lads laid in till about five that night. Lucky devils. They were on that night at Cavern as fresh as ever with no after effects. The Beatles have certainly gone up in my estimation. They are all great blokes with a sense of humour and giving one the feeling they are a real team."

For much of the early 1960s, touring became Mal's life. Against the wishes of Lily, left at home with Gary, Mal gave up his job at the Post Office in order to be at the Beatles' beck and call full time, clocking up industrial levels of mileage driving from Liverpool to London. He was also expected to attend to almost every personal whim.