Ok, now wirex partially solved the problem.
Today 26/04, 11:25 AM:
coingecko 998 GBP/BTC
coinbase 1001GBP/BTC
wirex 991.01 GBP/BTC
0.7% of real exchange fee
Thank you, you noticed

We are working hard to listen to our community.
HOWEVER, if I want to exchange 0.1 BTC to GBP it uses the exchange rate of 953.23 GBP/BTC. If I exchange 0.11 BTC up to 0.5 BTC, the exchange rate is 976.71 GBP/BTC. I didn't put more than 0.5 BTC in my wirex wallet to test when (which BTC amount) the exchange rate actually reaches the 991.01 GBP/BTC.
It's a change in the logic. You can learn more about it here:
https://wirexapp.com/blog/wirex-v2-1-released-today"
Right now I tried to do 3 exchanges (1 through the site and 2 through the app), all failed. Furthermore, the 0.508 BTC I used to do the exchange are gone and no GBP appeared. I'm sending a message to support and I hope I don't lose 0.508 BTC. I'll post the results here.
That must be a glitch. However, you have nothing to worry about. Please give me your support ticket number and I will track the issue with the support team
I've notified the support and I've received a couple of emails informing that it is under analysis. Actually, I checked again the BTC amount and it was 0.5048 BTC not 0.508 BTC. Anyway, here is my ticket: #92417.
Wow, that news is from today, this change is happening on the fly! I'm glad to see the exchanges rates are better! Could you tell us how this fee is calculated exactly? Or what is the minimum BTC amount to get the highest exchange rate?