Now have retirement visa based on money in the bank here. Am I allowed to move this money to a fixed two year account at the same branch and live off money in savings accounts here? or do I actually have to show I am living off the money in the account I used to base the visa application on? Many thanks for your help as always.

According to Phuket Immigration, absolutely "yes".

You are free to do what you want. Just have the funds at the required level three months before next extension of stay. They normally do accept fixed deposit accounts in Thailand as you can always access them if required. You do not have to show yourself using the money.

As long as you have sufficient funds in the bank for the 3 month period prior to renewal of extension you can put the money where you want. Fixed deposit accounts are usually accepted by Immigration.

Yep. Most offices will accept a fixed account. Always worth asking your local office though.

Phuket immigration will not accept a Siam fund account the money has to be in a savings account. This all so confusing so I should ask your local immigration office.

A fund account is not instantly accessible while fixed account is.

I have been using a Bangkok Bank Fixed Deposit Account for five years with no problem.

As has already been said, ensure a balance of 800,000 Baht or more for a full three calendar months before you apply for your extension renewal.