Earlier quoted context omitted.
Except the UK and US security agencies share data freely through the Five Eyes alliance. https://en.wikipedia.org/wiki/Five_Eyes
Yes, and as UK citizen I can hold my government to account through the democratic process if they start freely sharing data on UK citizens to others in the Five Eyes alliance. Notably the Five Eyes alliance used this exact setup to avoid local laws and democratic accountability, I don't want it to be easier for it to continue. I sure as shit can't hold the US government to account.
How will you know?