The Liberal Party was pushed to the left after 1900 by the strong influence of the 'New Liberal' ideas of people such as Thomas Henry Green, L.T. Hobhouse and John A. Hobson, and by the perceived need to come to an agreement with the nascent Labour Party. Here is an excellent article entitled
The New Liberalism:
http://www.liberalhistory.org.uk/item_single.php?item_id=85&item=history .
The pact agreed in 1903 between Herbert Gladstone and Ramsay Macdonald meant that Liberal and Labour candidates in parliamentary elections would not compete with each other. It broke down before the 1918 general election during the First World War.
The article
The New Liberalism identifies the disastrous result for the Liberals in the 1895 election, when they lost over 100 seats, as a contributory factor to the rise of New Liberal ideas in the party. The 1895 election happened because the 1892 election resulted in a Liberal minority government with Irish Nationalist support. By 1895 Lord Rosebery's government had lost the will to live and Rosebery used the defeat on the relatively unimportant issue of increasing the budget to buy cordite for explosives for the army as an excuse to resign.
So if in 1892 the Liberals won an adequate majority without needing to depend on the Irish Nationalists, they would be able to stay in office for a full term, which was legally seven years, but in practice five or six years. So that would be until 1898 say. If the Unionists (Conservatives and Liberal Unionists) win an 1898 election with a good majority, but not a landslide as in OTL and the Boer War happens as in OTL, the Unionists would be very unlikely to call a general election in 1900, as they did in OTL, because it would look to much like taking partisan advantage of the war. So the next election would be in 1903 or 1904 with either a Liberal or Unionist victory.
I don't know what proportion of Liberals elected in 1906 were 'New Liberals' (NL) and what were 'Gladstonian Liberals' (GL) and to what extend retiring GLs were replaced by NLs.