Voracious Heathen Chinee crustaceans are depleting the racial purity of Britain's native fauna. The mitten crab, whose Fu Manchu fingernails are insidiously cloaked in a silken covering, has been eating its way through Lincolnshire's salmon, shrimp and trout almost as calamitously as if it were human. Fortunately a hostile environment is being prepared, with specially designed river accommodation