"For individual membership you need to fulfill one of the following criteria :
Current or retired employees of the local government, medical or health services, civil servants, banking/finance, education, fire/rescue, police or post office. You may also join as an individual member if you are a dentist, pharmacist, optician, solicitor/barrister/magistrate or advocate, chartered accountant or engineer."
Thats the official line...however in the Watford branch, i know they are quite relaxed. It used to be fairly rigid at one time, not so much now..