@Bim ******
financial requirements for a Non-O for the purposes of retirement, from the UK embassy website:
"Financial evidence e.g. A copy of pension statement if the applicant is a pensioner, or a copy of 1-month bank statement showing your income from pension, or 3-month bank statement of at least ยฃ10,000"
However, their website is out of date so it's best to contact them to check first if you want to go this route.
Having said that, I think these have been the requirements for that visa for some years.