The news lopped 15p off the group's share price to 316p, reducing its stock market value by almost pounds 14m to pounds 328m.
Mr Evans, who made pounds 2.8m from exercising share options in the loss-making company last year, is currently a non-executive director at Chiroscience, but still owns 3.5 million shares worth slightly more than pounds 11m at last night's closing price.
He also has unexercised share options worth almost pounds 3m. Mr Evans' pay and fees dropped from pounds 109,000 to pounds 20,000 in the last financial year, according to the annual report, which was published yesterday.
Mr Evans, who will retire at the group's annual general meeting next month, is thought to be leaving because of other business interests. He has committed himself to revitalising the Toad car security company, where he is chairman. Toad's shares crashed earlier this year following the sudden resignation of its chief executive, Charles Parker, after only six weeks in the job. Last week it announced a marketing tie-up with Noel Edmonds, the former disc jockey.
Mr Evans claimed in February that he was "at saturation point". He also has a string of biotech company start-ups to his name, and three visiting professorships. He recently pledged not to launch another new venture for at least five years, although he suggested that Enviros, his fledgling environmental products and services group, was likely to float on the stock market in 18 months to two years.
Separately, it was revealed yesterday that Andy Richards, another founder of Chiroscience, netted pounds 1.38m from the company last year, having only joined the board in January 1996.
Mr Richards received a pounds 1.19m windfall from cashing in options on top of pay, bonuses and pension contributions, which rose to pounds 186,000 from pounds 89,000 in 1995-96, when he was only on the board for two months.
John Padfield, chief executive, saw his total pay package jump 47 per cent to pounds 371,000 last year, including a bonus of pounds 92,000.Reuse content