Update
I have received an update from Paypal regarding Sandbox Website Payments Pro (WPP) for the UK, and in spite of some information to the contrary, I am told that Sandbox WPP is not supported for UK accounts.
With this in mind, i created a US account in the sandbox and went through the eCart checkout wizard for WPP US.
It seems i can process a fast paypal checkout, but a credit card payment fails.
I looked at the 'how to debug a failed transaction' but when i try to add a payment response binding, I can't find one for website payments pro (US)