Ok, so my previous post was deleted, I don't know why. I tried to send the moderator a message asking why so at least I don't make the same mistake, but my messages to him/her are blocked. So I'm putting the numbers here again and expecting that it wasn't deleted because of the information my post contained (otherwise it would be censorship?):

At April, 20th:
Coingecko marked 963 GBP/BTC, at the same time, if the loading option was used to load BTC from the Wirex wallet to GBP at the Wirex card the exchange rate was 885 GBP/BTC, which means a real exchange fee* of about 8.8%

Now, April, 25th:
Coingecko: 977.99 GBP/BTC
XE: 981.541 GBP/BTC
CEX.IO: 997.49 GBP/BTC
Wirex card load GBP from BTC option: 917.53 GBP/BTC
Real exchange fee*: 6.69% (using the coingecko exchange rate)

By "real exchange fee" I mean what we lose in comparison to the "official" value of GBP/BTC or what we lose by not buying GBP from localbitcoin. In the end, it is this real fee (the ones the users "feel") that counts.

Finally, wirex site says "No hidden fee" at the card section. But I searched the site for what exchange rate is used to load BTC->GBP and which fees applies but I couldn't find this information anywhere at their site.