Thank you all for your valuable input. After a painful few hours I did manage to get it open. I used timber clothes pegs for wedges and a coat hanger. The key to all this is to cut the end of the coat hanger at an angle to give a sharp point which allows it to dig in and grab the door button. Don't expect this to be a quick job and to be free from paint damage. My car is a personal import entry level Toyota Celsior LS400, which I think made it easier to get into as I have no alarm or key-less entry.