What have Joe Cocker, The Grease Band, Paul McCartney and Wings, Roy Harper, Marianne Faithfull, Leon Russell, Ronnie Lane, Donovan, Andy Fairweather-Lowe, Spooky Tooth, Viola Wills, Bobby Harrison, Gerry Lockran, Hinkley's Heros, Eric Bell, Frankie Miller, Denny Laine, Eric Burdon, Tim Rice and Andrew Lloyd Webber, Pink Floyd, Sweeney's Men, Eire Apparent, Last Bandits, Rosetta Hightower, Fleadh Cowboys, Teresa Brewer and Terry Clarke all got in common?