The by-election was held to fill the vacancy caused when the 67-year-old[2] Conservative Party Member of Parliament (MP) Sir Hildred Carlile resigned from the House of Commons on 20 November 1919 by the procedural device of accepting appointment as Steward of the Manor of Northstead.

[3] Carlile, who had held the seat since the 1906 general election[2] (and was returned unopposed in 1918[4]), cited ill-health as the reason for his departure from politics.

[10] The old parliamentary borough of St Albans, which returned two MPs, had been disenfranchised in 1852 after a Royal Commission had found proof of extensive bribery.

It had returned Conservative MPs at every opportunity since the 1885 general election,[12] apart from a two-year interlude when the Liberal Party won a by-election in 1904.

The Representation of the People Act 1918 had nearly tripled the electorate nationally[13] by expanding the franchise to include all adult males and women over 30 who met certain conditions,[14] while boundary changes in the same Act had seen Radlett, Hemel Hempstead and Harpenden moved out of the constituency,[9] Radlett and Hemel Hemsptead having been seen as Conservative strongholds.

The former Home Secretary Herbert Samuel spoke for Gray,[15] while Nancy Astor came to back Fremantle,[15] who also received a letter of support from the Conservative leader Bonar Law.

[15] Brown was joined by the dramatist and Fabian George Bernard Shaw,[10] and by the former ministers Sir Leo Chiozza Money[10] and Arthur Henderson.

[1] In speeches after the count, Fremantle pronounced himself pleased with the result, and said that voters had sent a message of support to the Coalition for carrying on government "in accordance with the great traditions of the British Empire".

[1] Brown said that he was delighted with the result, which showed that the professional classes were coming round to supporting Labour;[1] and Gray said that he could take defeat in a sportsmanlike manner.