A few possibilities come to mind.
1. The Cromwell Rebellion either never falls and it's revolutionary attitude is corrupted by authoritarianism overtime. Or once it falls Parliament begins a series of reforms to ensure it doesn't happen again, planting a foundation for a slide to "anti Cromwellian" authoritarianism.
2. The loss of the 13 colonies lead to the military given more leeway to properly nip rebellions in the bud, and this plants the seeds for radicalism in the following decade, with pre-emptive crushing of dissent and invasion of countries that could fund those revolts (I.E France and Spain).
2. The British suffer much more in the Napoleonic Wars and emerge wanting to crush anything remotely resembling Napoleonic Ideals, which takes the moniker of "Communism" in which anything the Brits don't like become Napoleonic Filth, even basic Parliamentarian Rights, which must be cleansed and contained by any means necessary.