[tialaramex]

The Government wrote themselves a law (the "Investigatory Powers Act 2016") that says the Home Secretary can write to a service provider and ask them to record all the connections made.

Some of Britain's smaller IPSs don't like this sort of stuff (e.g. Andrews and Arnold's "implementation" of the government's opt-in child friendly censorship was to have a checkbox on their application page, if you say you want censorship it says you should choose a different ISP...), and so the smart money is on them having not written to ISPs at all. The backbone providers are few, bigger, and much more corporate. No colourful personalities apt to make the government look a fool in a televised hearing. So any letters probably went to the backbone providers although so far as I know none have come forward to say so.

In 2017 the ECJ told the UK government that such mass surveillance is prohibited, and it is also widely rumoured that the government then told the backbone providers to pause the collection.