Maybe you can use some German bank. They allow one to interact with their API for free. I use GNU cash for it. Though I doubt that you can file your taxes via GNU cash and be aligned with current UK law. You would need to check it for your own.
7dev7random7
joined 1 month ago
https://www.aquamaniac.de/rdm/
Gives you an adapter and an standalone tool. All banks should use the same API, apparently.