Crayfish

Chris Monk wrote: Incidentally legally if you capture an alien crayfish (by whatever method even when doing a newt survey) officially you are breaking the law (Wildlife & Countryside Act) if you release them back into the stream or pond they came from. Cooking them is one way to overcome this but make sure they are one of the 3 or so alien species first!

It's also against the law (Prohibition of Keeping of Live Fish (Crayfish) Order 1996) to keep them alive unless you live in certain parts of the country that are already especially infested, or are temporarily holding them 'for no other purpose than direct human consumption'.

Anglers have been recommended to kill them on sight, rather than moving them while alive.