This episode takes places during the winter of 1962-63, known as the Big Freeze of 1963, which was one of the coldest winters on record in England. According to the records of temperature that date to 1659, only the winters of 1683-84 and 1739-40 were colder. The cold was so extreme that in Kent, the English Channel froze for a mile away from the shore.
To coincide with the Christmas Special, Jenny Agutter (Sister Julienne) wrote an article for 'The Times' newspaper about her own memories of that winter when she was 9 years old and studying at ballet school. She recalled it being a fun and 'wonderfully disruptive' time for children.
Mabel Tillerson mentions splurging on a 'titfer' to spite her dead husband. This is Cockney rhyming slang for a hat (tit-for-tat = hat).
Mabel is played by Anita Dobson who previously played the role of Angie Watts in EastEnders (1985). Her onscreen husband in Eastenders, Den Watts, was portrayed by Leslie Grantham. Leslie Grantham is the real-life father of Daniel Laurie, who plays Reggie.