The head of Hampstead School, in north London, says: "I couldn't do without my early morning swim.
"I swim in the school pool around 7.30am for half an hour. It's the best thinking time and makes me feelquite different about any day. It gets oxygen to the brain.
"It's a very creative time, you can let your mind range freely. I really notice if I don't manage to do it."
DAME TAMSYN IMISON