I signed up for the Electrifix a few months ago, and Im not a member of a scheme or JIB.
I hadnt actually planned on doing it, but while buying some parts in my local Screwfix (Kingston upon Thames), the guy behind the counter asked me if i was a sparky, I told him yes, and he asked me if i wanted to sign up for Electrifix and get a possible saving of up to 20% on all future purchases.
He asked me what qualifications i had, and told him i had City and guilds parts 1 and 2 in electrical installation, he then made a phone call to the appropriate department, and that was it, i was all signed up just like that.
He didnt even ask me for proof of my qualifications, he just gave me the benefit of the doubt, and didnt even ask if i was the member of a scheme !
And yes as others have asked, you still get a discount even if you just go into a normal Screwfix branch, I bought a set of drain rods a couple of weeks ago, and the invoice printed out as an Electrifix one with a discount included !