Obtaining a work permit

Most people in your position work under the radar without work permits. 

Work permits are issued to people working for a company and not someone working out of their home.

Starting ones own limited company is possible but requires large capital investment and you can only own 49 percent of the company.  The remaining 51 percent must be Thai owned.  It also requires a minimum number of Thai employees and office space.

Coming by a work permit is still not easy, and you'll need a Thai lawyer to ensure the company and work permit are done properly. In addition many sectors are reserved for work by Thai nationals only, so foreigners are restricted in the types of business they can run. Permits are issued for specific hours and types of work, and the entire process must be repeated from scratch annually.

thanks for your reply Straydog. It seems to be quite a tough situation for me. The work I do in the UK can be done from anywhere and It may not be much of a risk to do the work from another country but I would be uneasy about trying to find new customers in thailand without the correct work permit

Straydog's right - just work under the radar.  Online work is probably one of the best ways to make money while living IN Thailand since you generally need a work permit otherwise.  This way you can skate by the permit requirement. If you are trying to gain Thai customers, then if any real authority questions you about it then you could pretty much dismiss it as a business transaction and more of personal transaction or something like that.