[1] The constituency returned one Member of Parliament (MP) to the House of Commons of the United Kingdom, elected by the first past the post voting system.

The two-way contest was dominated by the contemporary debate between free trade and tariff reform, and fought with the assistance of the major national organisations on both sides of that divide.

He and his brother Alban (an MP for the City of London) were partners in the firm Antony Gibbs & Sons,[3] which had organised the sale to the Admiralty of two pre-dreadnought battleships built in England for the Chilean Navy, in order to avoid them being sold to a rival power when Chile did not complete the purchase.

The Conservatives and their Liberal Unionist allies were split on the issue of "tariff reform", a form of selective protectionism promoted by Joseph Chamberlain as Imperial Preference.

At the meeting in St Albans on 23 January when he was selected, he described Chamberlain's policy as "retrograde, mischievous, and ruinous for the country and the empire", pledging himself to oppose protective tariffs, no matter what they were called.

[12] Slack was assisted in his campaign by the Free Trade Union, who established an office in St Albans in late January, and organised a series of meetings.

[18] Incensed by Gibbs's vote against the Church Discipline Bill in 1899, and buoyed by their success in other recent by-elections, they prepared for an "active crusade".

On 3 February, Frederick Halsey addressed a meeting at St Albans in support of Gibbs, who deplored the destruction of local industries by "unfair foreign competition".

[9] The next day, Lewis Vernon Harcourt addressed a large Liberal demonstration in St Albans, telling the crowd that the Tariff Commission was a caucus of manufacturers and traders trying to corner supplies and swell their profits.

[9] Meanwhile, the Liberals secured the support of the Postal and Telegraph Clerks, the Workmen's National Housing Council, and the Amalgamated Society of Lithographic printers.

[20] The agricultural labourers had traditionally voted Liberal, and were considered unlikely to change, while the heavily unionised personnel of the Great Northern Railway at Hatfield were expected to support Slack.

When Lloyd George left the meeting, he required a police escort to pass through the crowd, and despite the protection of stewards and bodyguards his carriage was lifted off the ground by protesters.

[21] The Liberal agent, Mr W. Bernthal, wrote to the local representatives of the Tariff Reform League, excusing them from any blame for the disorder.

On Wednesday 10 February, Gibbs spent most of the day with farmers at the weekly market in St Albans, while Slack toured some of the city's major businesses and addressed workers on the Midland Railway.

[23] In the evening, the Conservatives held a meeting of 3,000 people at the drill hall, where the principal speaker was Sir Robert Hermon-Hodge,[23] the MP for Henley.

[25] Gibbs visited polling stations at several towns near St Albans, and in the afternoon returned to the city to address the workers at Dangerfield's colour printing works.

Roads were flooded in many places, and many of the motor cars which had been engaged to bring voters to polling stations were unable to make the journey.

[27] The downpour was thought by both sides to have considerably weakened the Liberal chances of success, because although a high turnout was expected, the rain made it impossible for many working class voters to travel to the poll.

[14] Slack did support the Trade Disputes Bill at second reading,[29] but held the seat for less than two years, until his defeat at the general election in January 1906 by Hildred Carlile.