What are the financial requirements for obtaining a Non-O visa in Thailand with a pension income?

Only way to find out is ask the Thai Embassy in London

Isn't the issue that if you arrive on a 90 day O Visa, that when you extend it after 90 days you can only show/use the 800.000 scheme? The 65.000 Baht pr month has to begin 1 year before extention, or am I missing something?

To apply for a 90 day Non-O visa in the UK you need to show an income of £1,500 per month (doesn't need to be restricted to pension) or a sum of at least £18,000. Once you get to Thailand you can apply for a 12 month extension of stay when you are down to the last 30 days of your entry stamp but you will need to show a minimum of 800k baht in a Thai bank account for at least 2 calendar months before applying

60,000 pa is not enough you need to use the 800k method

You normally need to document three months of income of at least 65,000 baht per month to apply for a Non O visa. Otherwise, you must use the lump sum option of 800,000 baht. (Some foreign missions also accept a combination as long as it totals 800,000 baht, but I’m not certain whether the UK does).

In Thailand, you must document 800,000 baht for the first year. For subsequent extensions, the general rule is at least 65,000 baht per month, but here too some immigration offices accept a combination if it totals 800,000 baht over the year. This must be clarified with the specific immigration office you will use.

P.a?

p.a means per annum - which means per year.

Surely you mean per month?