The "tank" that Steed is caught and miniaturized within is actually a six-wheeled armored personnel carrier (APC), called an SV603 Saracen, built by Alvis and used by the British Army in the 1960's.
About this time, it was rumoured that Jane Merrow would be the actress to succeed Diana Rigg, who was due to leave the series. She was one of Patrick Macnee's favourite performers.
The giant calendar is the same one previously seen in Death's Door (1967), even showing the same date.
The only episode of the Emma Peel seasons, where John Steed is on the crime scene, at the beginning, without Mrs Peel but with supporting characters.
One of the thugs guarding Mrs. Peel was reading "The Novels of Jane Austen"