No, you can't use a British Visa card to pay for things on a Japanese account- they will only accept cards issued to addresses in Japan. Your best bet for being able to buy games from the Japanese store is the eBay method I talked about above. Go to eBay and search for PlayStation Store Network card and you will find him. You would be able to pay him via PayPal (which can be funded through your credit card) and he'll send the code along with directions on how to enter it in.