One of the provisions made by the data protection act is that you can check whether any data held in any database about you is correct or not, them refusing to tell you what data they hold on your is a breach of the act.
This wikipedia page should give you some idea of your rights under the data protection act, bear in mind this is wikipedia though.
If fraud has taken place and Paypal are not being cooperative, involve the Police and cause Paypal as much of a headache as you can. You may not win the fight against Paypal, but I'm sure you can cost them more than the £10 they have unjustly taken from you.