Pro-Brexiteers have often cited stronger bilateral ties, such as those with the US, as an advantage of Brexit. And of course, post-Brexit, Britain will be ever more reliant on the willingness of countries such as the US to cut deals with them. As an independent negotiator in these new deals, Britain will have less power to push back over silly things like data privacy; and as a member of Five Eyes anyway, they're all too happy to have the US do their spying on their behalf, just like the US likes Britain spying on US citizens to the US Government's benefit.
The recent Huawei 5G drama does seem to go against the grain of this. After all, if the UK had less power to push back, then clearly nobody has told them.
Although if you look at the actual text on the UKUSA agreement document HW 80/2 [1], rather than the short synopsis from Wikipedia, it says very clearly that the UKUSA agreement covers only sharing of "foreign communications" where footnote 3 on page explicitly excludes communications of both the UK and the USA.
Optic Nerve was one of these things. Basically, GCHQ or NSA hacked Yahoo!, GCHQ used that to collect stills for every single webcam feed on the platform (this! was! back! when! Yahoo! was! still! relevant!), including a lot of intimate photos, so on. Lots of fun stuff there!
But that's a modern example. There are some pretty interesting ones. Here's a fun list of some celebrities that were the targets of a Five Eyes country and were spied on by multiple agencies as a result:
