What options do I have for extending or renewing my Non-B visa while I will be in the UK?

The original poster is facing an issue with their Non-B visa expiring on September 15, but they need to be in the UK from July 20 to September 20. They are seeking advice on whether they can apply for a short extension before leaving Thailand, if others have successfully renewed their Non-B visa in London, and what their options are. Responses indicate that there is no short extension available, renewal cannot be done outside Thailand, and they will likely need to start the visa process over upon return to Thailand or find options to apply for a new visa while in the UK.