Veteran British actress Prunella Scales is suffering from a form of Alzheimer's disease.

The Fawlty Towers star, 81, has opened up about her condition in a new documentary which she has filmed with her actor husband Timothy West.

In the film, which documents the couple's passion for travelling by boat on Britain's canals, West reveals, "Pru has this condition. It's sort of Alzheimer's but it isn't; it's quite mild... She can't remember things very well...

"When you think back over the long period and you think this person that I loved and enjoyed this and that and the other with doesn't really exist any more, it's another person... that's quite painful. But you mustn't think like that, you must take it from day to day. You notice how much she's able to do and how much she enjoys life.... Her sense of humour is still there, and things still make her laugh. We have a lot of fun."

Scales brands her condition a "nuisance", adding, "We're determined to make the most of it (life) while we still can."

The couple has been married for more than 50 years. Their documentary, Grand Canal Journeys, airs in the U.K. on 10 March (14).