What do the errors say, exactly?
Have you tried paying using a browser to sign in to ebay.co.uk? Even if a browser does not work, it may provide a more explanatory error message.
Have you verified that the seller ships to the UK? If the seller is new to selling or located in another country, the seller may not have set up the account to accept your payment.
Have you checked your PayPal account to make sure everything is up to date?
Tried another credit card or payment source?
