Love free-for all: The band in the Seventies (from left), Stevie Nicks, Mick Fleetwood, Christine McVie, John McVie and Lindsey Buckingham

Fleetwood Mac were sitting around stoned in the studio one night with one of their engineers when they set about solving an arithmetic problem that had been niggling at them.

How much cocaine, they wondered, had drummer Mick Fleetwood put up his nose? Working on the premise he had taken an eighth of an ounce every day for 20 years, the sound engineer calculated that if you laid out the drug in a single snortable line, it would stretch for seven miles.

Rock ’n’ roll is full of such apocryphal stories, but as Fleetwood admits in a candid new memoir, this one is completely true. But then, this is the band that in 1977 gave the world Rumours, one of the best-selling albums ever, and almost died in the process.

Though they appeared deceptively inoffensive, with their hippy-ish outfits and gentle, melodic hits such as Don’t Stop, Little Lies and Go Your Own Way, when it came to decadence and over-indulgence, Fleetwood Mac made the Rolling Stones or Led Zeppelin look like a Salvation Army band.

Quite how they are still alive, still talking to each other and touring is a marvel to everyone, least of all themselves. It is a puzzle that Fleetwood, 67, tries to explain in his autobiography, Play On.

He claims in his new book that he ‘refuses to be romantic in my perspective of drug abuse’, but admits ‘it was all new and undiscovered territory’ when he first bought cocaine in 1975.

After innumerable line-up changes and personal tragedies, the band had taken on two new American recruits. Singer Stevie Nicks and guitarist Lindsey Buckingham, who joined as a romantically attached couple, injected Californian glamour into an otherwise all-British band made up of bassist John McVie, his wife and singer Christine, and Fleetwood, the 6ft 6in son of an RAF fighter pilot and the band’s drummer and de facto leader.

The act, originally a Sixties London blues band, were to become a huge pop success with their album Fleetwood Mac. It was recorded at Sound City in Los Angeles, at a time when the city was hit by the ‘first wave of the tsunami of white powder that rolled in’ during the Seventies and Eighties, Fleetwood recalls.

Cocaine was dispensed at the studio ‘as if it were simply another of the available services at your disposal’, and the album was written with ‘white powder peeling off the wall in every room of the studio’.

A studio engineer would test it for purity, which the wide-eyed Brit compared with a ‘cool’ chemistry lesson.

That album went to Number One in the U.S., and the fact that the band’s creative juices had been stimulated by drugs and drink encouraged even greater excess next time around. Making their following album, Rumours, ‘almost killed us’, says Fleetwood.

By the time they started writing the album, he claims, ‘we had all fallen to pieces’: the McVies were ending seven years of marriage and only spoke to discuss music, while Nicks and Buckingham had also broken up.

Fleetwood’s marriage to Jenny Boyd, sister of George Harrison’s first wife, Pattie, was heading for divorce. And Christine McVie was having a fling with the band’s lighting director. All this was worsened by creative tensions, the temptations of their new-found wealth, and by the band’s astronomical drug and alcohol consumption.

The solution to the various relationship breakdowns, they decided, was to live together in two groups — the men sharing one flat and the two women in neighbouring ones elsewhere.

At the studio, Fleetwood would go from room to room trying to keep spirits up. When his good humour didn’t suffice, there was always cocaine — lots of it

‘In the studio, we had a ritual, in which the engineers and band members all started humming a tune — it changed over the years — which would serve as a siren’s call for cocaine, specifically the cocaine that I was invariably holding,’ writes Fleetwood.

The tune in later years was often Vangelis’s theme to Chariots Of Fire, to which the athletes run in slow motion.

‘As if in a trance, I would drop what I was doing and in slow-motion, beckon them over,’ recalls Fleetwood. In ‘homage to the film’, he would make them run in slow motion, ‘then get them on their knees and beg, before I’d administer the goods’.

In those days, they would even include a ‘thanks’ to their drug dealer on their album credits.

Rumours took a year to record, costing more than $1 million. But the album, released in 1977, stayed at Number One in the U.S. charts for 31 weeks, and has sold more than 45 million copies worldwide, producing a slew of chart-topping singles. Most of the songs were all about the band members’ break-ups.

The lesson was obvious, said the gorgeous Stevie Nicks: Fleetwood Mac created its best music when the members were suffering the worst personal crises.

The decadence — amazingly, all claimed against tax as ‘corporate expenses’ — continued on tour, Fleetwood says. The band’s ‘rider’, the requirements it laid down before each performance, was ‘extensive, detailed and exhaustive’. The band demanded 14 black limousines continually at their beck and call, while Nicks insisted her room be painted pink and have a white piano (a crane was often used to lift it through a window).

‘We were pleasantly out of control,’ muses Fleetwood. Cocaine was bought ‘in bulk’ and everyone — band and crew — would turn up each night and queue for their ‘ration’. The handing out of drugs was even listed on the band’s daily tour schedule.

Stevie Nicks: Fleetwood Mac created its best music when members were suffering the worst personal crises

Nobody consumed more than Nicks and Fleetwood. He admits that, as acting manager ‘through all of that wonderful chaos’, he would often go around bullying other people to give him any of their ration they hadn’t consumed.

The situation became even more complicated when Fleetwood and Nicks began an affair that lasted several years. They would ‘sneak away’ (which can’t have been hard given how stoned everybody else was).

When Fleetwood told Lindsey Buckingham he had taken over duties from him as the singer’s lover, he simply said: ‘Nice of you to tell me. I appreciate it.’

The sexual free-for-all took another twist when — having split from Jenny, who was looking after their two daughters in England — Fleetwood started a relationship with one of Nicks’s best friends, Sara Recor.

Fleetwood, a man who apparently didn’t know the meaning of the word ‘faithful’, admits he was ‘surprised’ that Nicks was ‘so hurt’. But at least, true to form for Fleetwood Mac, she was inspired to write a song, the hit single Sara.

Fleetwood and Sara, who eventually wed, were ostracised by their friends, including the rest of the band. That marriage lasted seven years, before, bizarrely, he remarried Jenny.

But their second union was no more successful than the first, and having divorced again, he married third wife Lynn, mother of their twin girls. You may not be surprised to learn that the couple are getting a divorce.

After all this marital chaos, Fleetwood still appears to have a lot of affection for Nicks, and even believes they were connected in another life. But she doesn’t appear to see it the same way, last year blaming cocaine for turning them into ‘nutcases’ who started an affair after they got ‘completely drunk, messed up and coked out’ at a party.

Last year she said their relationship was ‘a doomed thing and caused a lot of pain to everybody’.

Estimating that she spent $1 million on cocaine in the ten years she was addicted, she said she only kicked the habit in 1986 when a plastic surgeon warned that her nose might disintegrate. (She still has a hole bigger than a 5p piece in her septum.)

As hapless in personal finance as in love, Fleetwood says he never saved any money, and has no idea how much he earned or spent in those years. He went bankrupt in 1984, and says he can’t even remember how many times it has happened again since.

Cocaine: Nobody consumed more than Nicks and Fleetwood, who is pictured backstage here

As Fleetwood acknowledges in his book, the band’s bizarre saga of drug-induced disaster started long before Nicks and Buckingham came on the scene. He admits he and his bandmates failed to see that fellow founding member, the brilliant guitarist Peter Green, had mental problems. He blames these on the vast amount of LSD Green took — as did other band members.

Fleetwood recalls one ‘trip’ during a U.S. tour. Imagining each other to be terrifying skeletons, the band sat holding hands in a circle on the floor of a New York hotel room, passing around a telephone so they could each ‘blubber’ to the man who had supplied them with the drug.

Still rocking: Fleetwood on stage in New York last year. The band have 40 tour dates lined up in the U.S. and more planned in Europe

Fleetwood says Green’s behaviour ‘changed fast and drastically’. He started talking incessantly about religion and his disillusionment with the greedy, music industry. He wanted the rest of the band to donate all their profits to charity.

Green left the band in 1970 and became a recluse. He was diagnosed with schizophrenia and later threatened the band’s accountant with a gun for trying to give him royalty cheques.

He was only the first casualty of what Lindsey Buckingham has since called the ‘curse of the Fleetwood Mac guitarist’. Green’s fellow guitarist, Jeremy Spencer, the band’s other big LSD user, disappeared in 1971 in Los Angeles during the band’s U.S. tour, joining the Children of God, the sinister cult which used sex to win converts. ‘He’d been completely brainwashed,’ writes Fleetwood.

The next guitarist to come unstuck was Danny Kirwan, whose problem was heavy drinking. During 1972, just as the band was about to go on stage one night, Kirwan started ranting about a bandmate’s guitar being out of tune and then wrecked his dressing room.

He refused to play, and when his bandmates came off later and he tried to offer them tips on how to play better, his fate was sealed. Fleetwood sacked him.

Kirwan would later spend periods living rough in London.

His replacement, Bob Weston, had an affair with Fleetwood’s wife, Jenny. Weston died of a gastro-intestinal haemorrhage last year — within months, of another Mac guitarist, Bob Welch, committing suicide at 64 in his flat.

Despite all this death and decline, the five members of Fleetwood Mac from the Rumours era soldier on. Christine became the last to rejoin in January.