Thank you everyone for the advice on this, it has helped a lot. A full-time short course looks like the best option since I'll be able to learn quickly without having to re-cover parts of the syllabus that I may have forgotten over a long period of time. Also, it means that I would be less likely to change instructors over my training. The relatively low cost of gliding means that I should be able to complete the course using savings and then still have enough left to remain current.
Thankfully I should be within a reasonable distance of clubs which are close to sources of ridge lift hence I may be able to start training in late winter/early spring without suffering from delayed progress due to lack of thermals.