is this the 'snoopers charter' (2016 Investigatory Powers Act/Bill)...? where the ISP and Mobile Provider has to record all metadata for 24 months?
if so... I would of thought (being re-sellers) this would all be done by BT (that ISP, on this date, at that time, etc) - is it not? (in THIS situation where the ISP is a re-seller on BT Wholesale)
The backhaul network cannot tell and have no responsibility for what an individual user is doing, that's on the ISP. Its all just a bunch of packets going to the ISP as far as they are concerned.
An ISP cannot tell much of what a user is doing either without deep packet inspection and that's a huge waste of resources, never mind keeping a log of that data. Plus its really dumb as unless they are going to demand all data centres also log all traffic, just running a VPN on a cheap VPS bypasses it.
Even if they did, criminals need only rent a VPS in a country with no such laws and would still bypass it, so its just a huge breach of privacy for normal people and an extra cost for the ISP for no good reason.