The idea for Isis passing away was actually Hugh Bonnevilles. It had nothing to do with the terrorist group with the same name, but with the age of the dog. Since the dog who played Isis was around since the second episode of the first season set in 1912 he felt that it would be unreasonable for the dog to still be alive in 1924.
At 41:25 Daisy moans that Labour Prime Minister Ramsay MacDonald "seems to limp from crisis to crisis" and questions whether his government will last the year. This was rather prescient as the MacDonald government would collapse after only nine months due to the fear surrounding the alleged Communist threat which, the Conservative Party was quick to exploit.
Mary goes to the movies seeing a film starting John Barrymore. The only film of John Barrymore that came out in 1924 is Beau Brummel.