As for specific areas - I know Dorset has some - ask the local fishermen wherever you are.
I really want to try it in Poland but I can't figure out the legal status of using traps for one and I'm not even sure of the distribution of signal crayfish so until my polish is better i am going to have to wait.
Loads of freshwater rivers have crayfish - you need to as for permission though -
http://www.environment-agency.gov.uk/homeandleisure/recreation/fishing/38051.aspx
As for specific areas - I know Dorset has some - ask the local fishermen wherever you are.
I really want to try it in Poland but I can't figure out the legal status of using traps for one and I'm not even sure of the distribution of signal crayfish so until my polish is better i am going to have to wait.