Can a 12-month retirement visa be applied for in the UK or Thailand, and what are the financial requirements?

Q. Can a 12 month retirement visa be applied for in either UK or Thailand??

It depends on what exactly you mean by "retirement visa" whether available in UK or Thailand.

What you can apply for is:

- Non-OA (long-stay/retirement) that is valid for 1 year and gives you up to 365 days for entry, at the Thai Embassy in UK

- Non-O based on being over 50 (retirement/pensioner) that is valid for 90 days and gives you 90 days for entry, at the Thai Embassy in UK. You have to apply for a 1-year extension after.

- Non-O based on being over 50 (retirement/pensioner) that gives you 90 days for entry, at the local immigration office in Thailand. You have to apply for a 1-year extension after.

Q. Does one only have to confirm possession of the required finance ? Or must it be deposited in a Thai bank on the first year of obtaining the visa

You can use proof of income for visa application in UK. You need to have money in a Thai bank account in your name for a visa application inside Thailand or extension applications.

Here is a very rough comparison of retirement visas. You need to check again the detailed requirements at the Thai embassy in London website.