Because the new proposed rules require telecoms and ISPs to record and store all your on-line and telephone activity. The message itself is not recorded, but the sender, receiver, time and location are. Target stores can figure out if your teenage daughter is pregnant just from what she bought at their store, so there's really nothing at all about you that a determined data mining of ALL your online activity couldn't turn up.
The U.K. Home Office stresses it won't be reading the content of every Britons' communications, saying the data it seeks "is NOT the content of any communication." It is, however, looking for information about who's sending the message and to whom, where it's sent from and other details, including a message's length and its format.
The proposal, unveiled last week as part of the government's annual legislative program, is just a draft bill, so it could be modified or scrapped. But if passed in its current form, it would put a huge amount of personal data at the government's disposal, which it could use to deduce a startling amount about Britons' private lives - from sleep patterns to driving habits or even infidelity.
Which is utterly useless for catching criminals/terrorists before they do something. But it is awesome for rounding up all the friends and relatives of somebody who pissed you off.