I am a bit relucant to do because as well as my credit card details they seem to want all of my bank account details as well which seems a bit strange if I am paying by credit card.
As a side, the reason for this from PayPals angle is that your bank account is your default payment option (with Credit Cards being added as secondary options).
A more relistic view seems to be that they want you to only have one personal Paypal account, which corresponds with your personal bank account. You give your bank details when you sign up (useful as you switch funds between your Paypal account and your bank account) but its main use is for Paypal to check that the name on your Paypal account matches the name on your Bank account.
I got into an interesting situation when they discovered i had two Paypal accounts, as apparently i could have used them to launder money or something silly. Needless to say, my second Paypal account was quashed [:(]