I haven't read the legislation but I would fully expect that it would need a warrant to know the details. This sounds like they are formalising the collection of metadata rather than blanket access.
In the event of an actual terrorist, this gives them a lot of data so that they can argue they have the UK equivalent of probable cause to subpoena various sites for more detailed browsing history.
In theory, it would be something like "Crazy Joe Devola spent 16 hours a day at some hacking site. Better find out what he was looking at". In practice it will be "Facebook, give us access to his file"