I can only talk to you about China, but I believe that Thailand would be also a very good place to go with your minimum TEFL certificate. Most paces look for a degree and a 120 hour TEFL certificate. BUT, in China you could certainly try the non-government (i.e. private) schools such as Berlitz who might take you on an ad-hoc basis. Since you've been working in London, I presume you have business experience - Business English Teachers are in high demand by Berlitz and experience counts more than certificates.
If you do take private students make sure you charge up front - don't expect payment after they've walked out the door after a 2 hour lesson!!
Hope this helps a little.