Early in the movie, the informant picks tries to fire an empty Luger. He pulls the trigger twice, and each time there is a loud click. The Luger, as a single-action semi-automatic pistol, would not click when it's empty.
An establishing shot of the iconic revolving sign outside New Scotland Yard in Victoria and a zoom to a window several storeys up that building is followed by a view from Commander Swann's office which shows County Hall and the River Thames near Westminster Bridge, as seen from St Thomas's Hospital, about a mile away.
New Scotland Yard does not have a view of the Houses of Parliament or County Hall. The view is actually from the top floor of St Thomas's Hospital beside Westminster Bridge.
Det. Sgt. Jennifer Thatcher: My father flew with the RAF. He said there were only three things wrong with the Yanks: 'oversexed, overpaid and over here'.