"I sort of got disenchanted, I suppose," says Miss McKenzie, 68, whose last major stage role was The Philadelphia Story at the Old Vic in 2005 in which she appeared with Kevin Spacey . "I never thought I would hear myself say that, but I did not realise how much it would take out of me physically as I got older. It's too much."

The Olivier award-winning actress has told her agent to turn down all offers to act on stage and says that she plans to concentrate on television work including her role as Agatha Christie's sleuth in the forthcoming ITV series.

Miss McKenzie, who was especially admired for her work in Stephen Sondheim musicals such as Company, Follies and Into the Woods, says a factor in her decision to give up the stage was how few great roles there were on the stage for older women."I don't want to end up saying: 'The carriage awaits, my lord,'" she said. Happily, Maggie Smith and Judi Dench, both 74, have more staying power.

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