Depends what you are doing with them Monkey...
If you are talking about crayfish as bait, then you definitely cannot use them. Our native White-Clawed crays are protected (and rightly so). The American Signal Crayfish are also illegal to use. This has nothing to do with the issues on this thread, but is because the EA has deemed that as the signals carry a virus which kills our (rare) native species, they should not be used, as transfer of the virus to waters containing the White-Clawed species is possible. It also stops anyone using a native cray as bait, believing it to be an Americam Signal cray. Any caring angler will understand why the EA did this and I for one applaud it. See, anglers ARE conservation-minded humans after all, Shock horror!!