Young stars (clockwise): Emma Watson, Rupert Grint, Daniel Radcliffe

The 61-year-old will play young wizard Harry's friend Nearly Headless Nick, also known as Sir Nicholas De Mimsy-Popington.

Walters, 50, is currently picking up rave reviews for her role in Billy Elliot, in which she plays a ballet teacher who encourages a young boy to continue his dancing against the background of the 1980s miners strike.

She was nominated for an Oscar and won Bafta and Golden Globe awards for her part in 1983's Educating Rita.

More recently, she has appeared on TV in her former comedy partner Victoria Wood's BBC sitcom, Dinnerladies.

Now she joins Cleese, Robbie Coltrane, Alan Rickman and Dame Maggie Smith in the movie, which is being filmed in various locations in the UK, including Gloucester Cathedral, which stands in for Harry's school, the Hogwarts School of Witchcraft and Wizardry.

Young actor Daniel Radcliffe plays Harry Potter, an orphan who finds he has magical powers, and newcomers Rupert Grint and Emma Watson play his friends Ron and Hermione.

The film is due to be released in November 2001 in the US, where it will be known as Harry Potter and the Sorcerer's Stone.