Mary,I'm in Cambridge, so drop me a line ("rationalelectronics@yahoo.co.uk") if you want a natter.
I go to the Unicorn in Cherry Hinton (3rd Wednesday of the month) and the New Crown in Girton (3rd Thursday of the month). I'm planning, if I get time, to go to one at the Red Lion in Cherry Hinton this Wednesday, but I believe that's more a pub entertainment thing than an actual folk club.
Others I know of are the Portland Arms (never got round to going there yet) and the Stukeleys folk club (run by a guy who also comes to the Unicorn, but it's a bit of a trek for me). And there's a blues jam at the Boat Race on Sunday lunchtimes, IIRC.
Grab.