By 1910, (about the time that my Dad was born), Labour held 42 seats in the British Parliament.
And in the 1924 General Election they won 191 seats. Although this was not enough to provide a Parliamentary majority, Labour, under their new Leader, Ramsay McDonald formed a Government with the support of the (by now dying) Liberal Party.
Thus, Ramsay McDonald became the first Labour Prime Minister.
His Government lasted all of nine months (Jan - Sep 1924), but then lost a vote of confidence in the House of Commons, and was forced to resign.
By 1929 Labour was able to elect 287 M.P’s. Again, with support of the Liberals, Ramsay McDonald was able to form a Government, and for the second time he became Prime Minister.
Ramsay McDonald was seduced by power. Thus he opposed the General Strike of 1926, even though this strike should have been a Labour cause-celebre.
He was also unsupportive of the Jarrow march
http://en.wikipedia.org/wiki/Jarrow_March -- this too should have been a cause for Labour.
By 1931, with the dawn of the depression, Ramsay McDonald was persuaded to form a “National Government” of Labourites, Liberals, and Tories.
True red Labourites (my heroes) left the Party, but the National Government was elected by a super majority in 1931.
The “true Labour Party “won only 52 seats.
The “National Government”, though presided over by McDonald was in fact controlled by Tories.
The National Government, in its turn it gave way to the Coalition Government of Winston Churchill (1940 -1945).