Try local pubs and shops. My local shop employs students to work the evening shift. Also if your college has a bar or other student facilities you could see if they employ students to work there part time.
I've been on www.myparttimejob.co.uk and they've got some good jobs - mainly from direct employers rather than consultancies and they are all part time.
Thanks for that info - I've been to the job centre but wasn't very impressed with all the form filling and waiting around. A part time only job board sounds like the perfect option - will check out www.mypartimejob.co.uk now!