Is David Cameron (British Prime Minister) realistic when he proposes banning messaging apps?

The British response to the events in France last week is to seek the banning of messaging apps (WhatsApp, Snapchat, and others) because they encrypt messages – making it more difficult for the government to eavesdrop.

Here’s the link: NYTimes

Putting aside the utter impracticality of the idea – how do you criminalize applications that millions of people use?, and if one app can be written, so can a dozen more – what does this say about the British reaction?

Is a 100% surveillance society really in civilization’s best interests?

Who makes sure that the people doing the surveillance are, themselves, honest and above board?

Cameron, I imagine, means well. But is this approach realistic?