(With apologies if this question is answered elsewhere - I've not been able to find it.)

I currently have a one-year non-immigrant O-A long stay multiple entry visa, issued by the Thai Embassy in UK.

I will be returning to Thailand in the weeks before the final entry date on the visa.

At that time I plan to extend / renew my non-immigrant visa at Chiang Mai Immigration Office in Thailand to enable me to continue leaving and re-entering the country. I qualify for the over-50 retirement visa. I'm also legally married in the UK to a Thai partner of the same sex, though this is not currently recognised in Thailand, so the 'family' route does not apply.

I'd be very grateful for any advice on how I can apply for an extension or renewal, and what documentation I will require as evidence. Or, please point me to a webpage with all the relevant information.

Thanks, Tim

You will not able to apply for the extension yet, because when you return you will be allowed again for 1 year.

To travel and return again within this year you need a re-entry permit, single or multiple as needed. That can be easily obtained at the airport when leaving.

Only in the last 30 days of the year you can apply for an extension of stay at immigration In Thailand, for that you will need Bt 800,000, in a Thai bank for two months, or monthly income Bt 65,000, or a combination of the two.