IOTL Labour won the 1929 elections, gaining a plurality in parliament and allowing a coalition government with the Liberals. In 1931, with the Great Depression worsening, Labour leader Ramsey Macdonald went turncoat, created his own "national labour" party and formed a coalition dominated by the Tories.
So what if the Tories had won in 1929 instead? Presumably Labour would be thrust to a landslide in the next election, whenever it's held. And then Labour could press ahead with its agenda, similar to the one it passed IOTL in after 1945. And then there's the big thing: foreign policy. How would Labour handle Nazi Germany?