The best available rate and the mid-market rate can be the same in most cases, especially for liquid currencies like GBP, USD, EUR and so on. For these currencies, we are able to execute FX trades at rates very close to the mid-market/best available rate.

In markets where there are strong capital controls, parallel markets, etc., the mid-market rate may just be a rate that a Central Bank shares but is actually unattainable. The best available rate that we can get from our providers or internal liquidity might be very far off the mid-market rates that you see on Google, Reuters or Bloomberg.