I am considering getting away from the 800,000 in the bank for my retirement visa

What rate of exchange baht to the pound sterling does immigration base their calculations on, and is this variable.

Thanks

It varies but generally follows market rates.

I used this route recently and the charming lady, yes she was really nice, looked at the letter from the embassy, asked me what rate I was using, punched the figures into her calculater and said ok. She added that she was single, not sure why