I think if you're phoning an organiser and you're not well known, it's better to ask about the club and if it's possible to arrange an extended floor spot with a view to a booking. If clubs have a busy singers night you may be lucky to get more than 2 songs which won't do you justice if you just turn up on the night. We all have our "party pieces" which we trot out but you need to demonstrate that you can put three or four songs together with some interesting (but not necessarily funny) chatter between them to keep the audience with you.
The club I run is generally a singers club with no booked guests and I get the odd phone call asking about bookings at which point I tell them how we run and so as not to waste their time or mine I usually say if you're in the area then please pop in if you're free but it won't be for a booking "audition". Very occasionally I've had someone on for half a night - the most recent being in October when Bryony asked if they could do 4 in each half as they had a free night during a run of proper bookings in the area. We agreed a reduced fee and I actually gave them more in the end because we had a good night but they are few and far between.

Good luck anyway Faye with your quest for fame and fortune on the British Folk Club scene - well fame anyway! Whereabouts are you based by the way?

Cheers
Mark