Do they know what they are doing?

The Guardian reports:

Theresa May is to propose a major extension of the surveillance state when she publishes legislation requiring internet companies to store details of every website visited by customers over the previous year.

I reckon that I must visit over 100 websites each day (including separate visits to the same website).  But, for the sake of argument, let us posit that the average UK user visits only 25 sites.  If there are 20 million users in the UK (and bear in mind that it is not just the visits of you and me that will be recorded but also those of all of the large and small businesses), that means about 500 million visits per day for the UK users as a whole.  Multiply that by 365, and you get the annual grand total of UK website visits of over 180 billion (or 180,000,000,000).

That amounts to an awful lot of data for the internet providers to store and organise in some kind of accessible format.  Even if the police or the security authorities were able to extract the date for one particular individual, they would still have to look through many thousands of website visits.

Is this at all practical?