This shouldn't surprise anyone - thanks to our colonial heritage Britain has always contributed disproportionately to SIGINT gathering as we have lots of locations dotted around the world that are well placed for data gathering.
Given the Royal Navy like to think they have the most skilled submarine service in the world, and we have a long history of maritime charting, it shouldn't be a huge surprise that if any country is tapping undersea cables that it is Britain.
There are also plenty of stories from years ago about undersea cables being tapped. So that is hardly a revelation.
I've talked with RN submariners who visited our homeport. I would certainly call them more skilled than the average USN submariner; they have a much smaller cadre and spend a lot more time on sea duty since they don't have to follow U.S. DOPMA requirements.
However they don't have enough spare submarines lying around to just convert one like the U.S. did for Halibut, Parche, or our current special projects boat.
Given the Royal Navy like to think they have the most skilled submarine service in the world, and we have a long history of maritime charting, it shouldn't be a huge surprise that if any country is tapping undersea cables that it is Britain.
There are also plenty of stories from years ago about undersea cables being tapped. So that is hardly a revelation.