@David *********
for the first year you will need 800,000 in the Thai bank account. It needs to be in for 2 months prior to applying for the one year extension. The None O that you get in the UK, is to allow you to open a Thai bank account, and deposit the money for 2 months. The visa issued in the UK is only for 90 days.
The O A is for 1 year, but requires insurance, and criminal records checks.