Paypal exchange rate

I recently made some payments with paypal that requires the GBP currency.
I have added the GBP currency to my Paypal account.
I have a debit and a credit card in GBP currency (HSBC) that I use everyday.
I was not able to add these cards to Paypal. The process return the error “This card is not accepted. Please use a different card”.

I noticed that Paypal apply a particular disparaging exchange rate.
I usually use this site, xe.com that is more accurate of Google.
I concede they can use a little different exchabge rate, just enough to not loose money, but these differences seems exagerate to me.

Date Paypal XE.com Google Paypal diff
12 Jan 2017 0.81837 0.85198 8.85 + 3.94 %
10 Jan 2017 0.8196 0.85181 0.85 + 3.78 %

To calculate the percentage difference I used this formula:
Diff % = ((official_rate-paypal_rate) / official_rate) * 100