What do all of these people have in common?
Lynn Redgrave
Cleo Laine
Elton John
Peter Ustinov
Julie Andrews
Twiggy
Roger Moore
John Cleese
Peter Sellers
Bruce Forsyth
Petula Clark
Leo Sayer
Spike Milligan
Dudley Moore
Glenda Jackson
Shirley Bassey
Lou Rawls
Gladys Knight
Debbie Harry
Paul Simon
Judy Collins
Johnny Cash
Joan Baez
Alice Cooper
Helen Reddy
Loretta Lynn
John Denver
Kris Kristofferson
Arlo Guthrie
Anne Murray
Linda Ronstadt
Diana Ross

answer,