in Thailand you will need a will for the courts and once they are happy with everything they will send the paperwork to your lawyer to help you with the bank because they will not give up the money until the court process has been done and you have the paperwork from the court
if you have any money available or property in England then you may need a will for the courts in England, the best thing to do is ring a solicitor in England to find out if they will accept any will you have written in Thailand