Well, I have to slightly disagree with this, based on this extract from Wikipedia:
Casting
The film used mostly young unknowns, among them Mark Lester (Oliver), Shani Wallis (Nancy) and Jack Wild as The Artful Dodger, but also featured Hugh Griffith, an Oscar winner for Ben-Hur, in a cameo role as the Magistrate. Harry Secombe, who played Mr. Bumble, was well known in Britain but not in the United States, and Oliver Reed, who played Bill Sikes, had just begun to make a big name for himself. Ron Moody, who was also well known in Britain but not the US, recreated his London stage performance, after Peter Sellers, Dick Van Dyke and Peter O'Toole reportedly turned down the role. Elizabeth Taylor turned down the role of Nancy as well. Julie Andrews was also considered. Director Reed also had Shirley Bassey in mind, but his choice was rejected by Hollywood studio bosses who felt that the public was not ready for a Black Nancy. Classical actor Joseph O'Conor, not well known in the U.S., played Mr. Brownlow.
It would seem that we're both right ..... ?
