If you are UK non resident for tax officially with HMRC then not sure why you would think any income generated outside the UK would be of any interest to them?
My understanding, and practice, is that as a non-resident you don't even need to disclose it.
Unless there is something else the worms should stay in the can.........
Edit - pretty much what @CharlieH says above.
Curious why you wait for 7 years before considering trying to reclaim presumably overpaid tax?