The 'family portraits' on the staircase all have Roger Moore's face.
The African Prime Minister's daughter asks Danny when he acts like a servant, where is he originally. Danny answers that he is Hungarian. Tony Curtis parents were Hungarian and he understood Hungarian around that time.
The red mini driven by Danny, when he is arriving as the butler, is the same car (BAP245B) used regularly by Jeannie in Randall and Hopkirk deceased. Annette Andre, who played Jeannie, also appears in 'Powerswitch', the next episode of The Persuaders!
When Danny Wilde saw the portrait of Lord Brett Sinclair's parents, it's actually the family portrait of Roger Moore himself and his wife, Luisa Mattioli with their children (Geoffrey and Deborah).
Judge Fulton is not in this one.