Jesus frickin' Christ!!
So the PM of Great Britain wants to restrict the use of encryption? What exactly is he then going to do about securing the online financial affairs and communications of British citizens? It MIGHT be feasible to ban or water down encryption if the British Government could A) consistently defeat cyber-crime and voyeurism targeted at British citizens and business an B) be trusted to use their own power to decrypt at will responsibly. However, they are definitely failing on A) and the signs that they can execute on B) are really unpromising.
Only a small portion of encryption performed in the world is used as a tool for terrorists and organized criminals to shelter the plans of their next atrocity. It protects the communications and property of British people, companies, NGOs and governments--in short, the entire British society. If you compromise encryption without solidly addressing internet security on some other front, then you are setting up the British people as digital lambs for the cyber-slaughter.