Perhaps two-party system was the wrong phrase (we aren’t completely two-party in the same way as, say, America), but if you look at the UK at a national level, the Conservatives and Labour are overwhelmingly the top two and have been for a long time, and the majority of national governments in recent years have been formed by either the Conservatives or Labour. To my knowledge, every government post-WW2 has been either a Conservative or Labour government, or at very least had one of the two as the larger party. Granted, that is English-centric, but to view the composition of the UK government at a national level, you have to be English-centric to an extent because England is by far the largest constituent country of the United Kingdom in terms of population.
I would also politely disagree with your notion that two dominating parties is a recent and short-lived phenomenon. 2010 and 2017 were notable recent exceptions to a decades-long norm of majority governments; those two elections were the first since 1974 to return a hung parliament, and that election was the first since pre-war years to return a hung parliament, I believe. Until the 2010s, hung parliaments were not at all common, and the result was typically a more clear cut Conservative-Labour face off, with the combined vote share of the two parties typically being at least 70%, often approaching or over 80%. 2017’s vote share for the two main parties was 82%, 2019’s was 76%, and you look back to the latter half of the 20th century, the combined vote share for the two main parties was routinely comfortably over 70%.
Whereas in 2024, it was 57%, which is the lowest combined Conservative/Labour vote share since 1910, and recent polling would hint at a combined vote share of potentially only around 50% or slightly higher in 2029.
For lack of a better term, my question is; could this trajectory be hinting at the end of the decades-long duopoly the Conservatives and Labour have had on forming government in this country? I do feel that the current polling numbers, and the trajectory from the last election, could be hinting towards the impending end of the Conservative/Labour duopoly that has largely endured since WW2.