I'm currently working on a tax-related app and needed HMRC's official exchange rates. As they're only offering XML downloads, I decided to create a small API which provides the data in JSON format.
I am just posting it here because I found the setup worth sharing as it's just a couple of static JSON files on a GitHub repository which updates itself every night through CircleCI.
Hope this is of any help to anyone. ️
https://github.com/matchilling/hmrc-exchange-rates