Just to be clear, Guya is the tax pro, not me, don’t trust anything I say.
I am simply reporting how the London firm that does our taxes files our taxes with HMRC and although they file electronically on our behalf we get a full copy of the self assessments, and the 15% tax free and reference to the DTA is clearly detailed in the filing. I promise that whenever HMRC deny that claim then I will be sure to report back here. No idea how many back years they would go after.
When we first moved back it was nice to only be taxed on 90% of my US private pensions but unfortunately that was stopped around 2018.