Hello Colin,
Thank you for your question about setting the default search country. It is now set to "UK" for you. Please note that if you re-authorize, it will overwrite the country with whatever you have specified in your eBay profile. So yes, you should change your default site to "UK" at My eBay to ensure that it doesn't flip back to the Thailand.
We hope we have resolved this to your satisfaction. Please advise if we can help with anything else.
bidslammer