interview by MATT SWEENEY portraits by ANNABEL MEHRAN In the late ’60s Fleetwood Mac, the band led by the guitarist and singer Peter Green, was one of the most influential groups in Britain. Their music was dark, heavy, haunted, minimal, hypnotic, and sexy. In 1970 Peter Green quit the band due to a nervous breakdown,but he left behind a template for his bandmates. In the following five years, during which the band made six albums, drummer Mick Fleetwood, bassist John McVie, and keyboardist/vocalist Christine McVie maintained the Fleetwood Mac sound using various front men. In 1975 they hooked up with Lindsey Buckingham and Stevie Nicks in Los Angeles and within weeks recorded one of the biggest-selling rock records of all time. Amazingly, the band achieved great success without having any management: Mick Fleetwood and John McVie steered the band through the ’70s, cocktails in hand. Fleetwood Mac never had…