One of the signs in the beginning of the episode has German and Russian writing on it. You'd expect the Russian to be a translation of the German, but it isn't. While the German writing informs you that you are entering East Germany, the Russian writing says that it is forbidden to carry a weapon without a proper (military or police) service ID card.
Danny Wilde meets with American agent Joe Pfeiffer on the centre-circle of an empty football ground to avoid anyone eavesdropping on their conversation. These scenes were filmed at Vicarage Road, the home of Watford Football Club.
The blue van appears to be the same one used in the Persuaders episode #17 "Five Miles to Midnight".
Judge Fulton was not in this one.