John, 1. Thai Embassies are not issuers of Thai traffic law. Information on traffic rules published on their sites are just unsubstantiated information. 2. It is international conventions on driving in foreign countries that the Thai (and many other Governments) signed up to. I understand that there are 2 of these conventions (the second updated the first). Nowhere in either convention does it even mention IDP's, let alone specify that they are required.
Crap. The Royal Thai Embassy in London is not an authority for Thai driving laws. The authority is the international convention of driving signed up to by most countries in the world, including Thailand. The convention allows tourist to drive on their national licence in Thailand. If their national licence is not in English, then an English translation is required (obviously, an IDP meets this requirement but an IDP is not required if the licence is in English).
Paul De Graaf Yes. IDP. It is a permit and definitely not a licence. It does not matter how long you have been calling it a licence, that is still incorrect. It remains a permit and will never be a licence.\
Yes. Visa exempt followed by an extension is meant to allow tourists to holiday in Thailand. If you desire to stay in Thailand for a longer period then you are no longer a tourist and if you do not wish to fall foul of Immigration, then you need to obtain a visa appropriate to your reason for staying.