Are you using the 800,000 in the bank or the 65,000 monthly, if using the 65,000 monthly method they will also want a 12 month bank statement showing your deposits. If this is your first extension on the 800,000 they might also want to see a statement showing that you had the money in the bank for two months. They will know what letter you need for Immigration, they do it everyday. It is just a letter certifying that the bank account is in your name only.