Good luck blocking a "because terrorism / why won't SOMEBODY think of the children" bill - similar legislation passed recently in Australia, and technically it is supposed to have been implemented by now, although many providers have requested extensions. Metadata stored for 2 years.
One of the issues here is the wide variety of different government departments that have access to this data, without needing a warrant:
List of agencies applying for metadata access without warrant released by Government - ABC News (Australian Broadcasting Corporation)
This isn't just catching the potential grooming of future ISIS members. I presume the same sort of "focus creep" is going to happen in the UK.