During the scenes where Drake is tailing Rawson, and Rawson catches on to him, several shots show in the background very rare glimpses of what was about to become the tallest building in London, the (as it was called upon completion) 600+ foot tall Post Office Tower, at that time under construction. Notable at the time was the fact that A) there was some controversy at the time about the purpose of the tower, to the point that hearings were held on the matter and there were attempts by the government not to allow the construction to be photographed, and B) there were serious inquiries made about how the construction crane at the top of the tower, seen in all the shots, was ever going to be removed from the tower upon completion of construction. Somehow, they managed to get it off successfully.
When Drake first meets with Gorton at M9 to discuss Rawson, Gorton describes Rawson as a 'lone wolf.' This was to have originally been the series' name - and, in fact, Danger Man was known in some markets as Lone Wolf.
In the scene early on, where Drake 1st encounters Rawson at the Star Tavern on Belgrave Mews West, SW1., the blonde girl, dancing around ('Sue' is the character's name) whom Drake bumps in to, is a very young 'Wendy Richards' - who will become best known as Miss Shirley Brahms, the ladies junior sales person at Grace Brothers, in Are You Being Served? (1972), and all subsequent projects related to it.
Sheila Allen will costar in an episode of Patrick McGoohan's next series - the classic The Prisoner - in the episdoe A, B, and C, as Number Fourteen.