Nowadays, British intelligence services have access to citizens' communications data, whether telephone calls, emails, Facebook messages or other forms of communication. Where video surveillance on the streets is concerned, surveillance has a long tradition here. Since 1926, an unassuming structure that was once billed as the world's smallest police station has stood at the corner of London's Trafalgar Square - a traditional rallying point for demonstrators. For a time in the twentieth century, it even had a direct phone line to Scotland Yard.