Do I need to return to the UK to apply for a METV if I hold a retirement visa in Malaysia?

No, you cannot renew a Multiple-Entry Tourist Visa (METV) in Thailand, but if you actually hold a retirement visa (such as a Non-Immigrant O or O-A extension), you renew that extension of stay directly inside Thailand at a local Immigration Bureau office rather than using an METV

No, holding a British passport does not strictly force you to return to the UK to apply for a Thai Multiple-Entry Tourist Visa (METV), provided you hold legal residency or a long-term pass in Malaysia.Where to ApplyCountry of Residence: Thai e-Visa regulations require you to apply through the Royal Thai Embassy or consulate in your country of legal residence.Using your Malaysian Visa: Because you hold a valid Malaysian long-term retirement pass (such as MM2H), you can submit your application via the Thai e-Visa portal assigned to Malaysia, proving your legal residency with your Malaysian visa sticker/endorsement.Key Requirements to Keep in MindProof of Residence: You must upload clear proof of your legal long-term stay status in Malaysia during the online application process.Supporting Documents: The embassy in Kuala Lumpur will expect financial proof (such as sustained bank statements) and travel intentions, though policies on local currency vs. specific home-currency equivalents depend on the specific post instructions.Application Restrictions: Do not try to apply via an online portal while physically outside of your declared region of residence or if local jurisdiction rules at the embassy dictate in-person submission for certain anomalous pass types.

You *might* be able to get one in Vietnam or Laos, there have been reports of non residents getting the METV there a few months back. Other than that it's a return to the UK