Date: It is late June 1916 leading up to the start of the Battle of the Somme (1st July).

Goof?: Hazel expects up to 30 people to tea. If this many did indeed turn up, the morning room would be full to bursting. (4'39")

Lady Prudence background: She has a cousin who is a bishop and lives in Henley-on-Thames (11'31").

The boating sequences were shot at Frensham Pond, near Farnham in Surrey.

Hazel background / goof?: Her father is now described as a "shipping clerk" (17'58"). In A House Divided, he was an "accountant". But maybe this is supposed to be a description of the same job, or else her father has changed jobs?

The song, If You Were The Only Girl In The World (after which this episode takes its name), was written in 1916 by Nat D Ayer (music) and Clifford Grey (lyrics). Reader Darrel C Karl adds that it was performed in the revue The Bing Boys Are Here, which opened at the Alhambra Theatre in London on April 19th 1916, two months before the date of this episode, and ran for 378 performances. At one point Hazel tells Lady Prudence that Jack Dyson took her to see The Bing Boys.

Celia Imrie (who plays nurse Jenny in this episode and Missing Believed Killed) is a familiar face, best known for her later work as a sidekick to comedienne Victoria Wood.

James background: He is now a major.

The sequences outside the chateau where Georgina is nursing were shot at Waddesdon Manor, near Aylesbury in Buckinghamshire, a National Trust property.

Georgina background: She can speak German (36'34").