I did the GDL part time, worked full time and emerged without any debt. It’s possible. Most of my classmates worked full time too.
If you have to go into debt, definitely try to get a career development loan. The interest rates will be much better than your credit card or overdraft (unless you can wangle a student-style interest-free overdraft).
One other option is a scholarship from an Inn of Court. Even if you’re ultimately not interested in going for the Bar, they’re not going to know that if you can present yourself credibly as a future barrister. You’ve probably missed the deadline for autumn 2010, but if you’re part time, there’s always next year. Not many people know about the Inns’ GDL scholarships, so the competition for them is much less intense than for the BVC/BPTC scholarships. It would also look great for your CV whether you go to the Bar or train as a solicitor.