Regular users of Tooting Bec Lido may have noticed a couple of swimmers doing more than their fair share of lengths up and down the outdoor pool in recent weeks.

The hard-working pair are Al and Lucy Petrie, who are aiming to become the first husband and wife team in history to swim the 21 miles across the English Channel within the same year as each other.

Their epic swim is in aid of Babyhouse, a charity they launched in 2004 to raise money for a £25,000 state-of-the-art incubator, which helps critically ill premature babies.

The pair will donate it to Chelsea and Westminster Hospital, where their own twin boys, now four, received care after being born at just seven months old.

The mammoth swim, and the training for it, is a far cry from the couple's usual activities. Al, 36, recently appeared in Channel 4's the Mark of Cain and Lucy is best known for her performance as Charlotte Lucas in the BBC's 1995 series of Pride and Prejudice, which starred Colin Firth and Jennifer Ehle.

"Maybe I'll swim across in a bonnet," joked Lucy, 40, of Rydal Road, Streatham, who will take the plunge in September, two months after Al attempts the swim. "Nine years ago I swam the channel in a relay with six people but it's an opportunity to inflate my ego by doing it solo."