British 1848 Revolution?

If I remember rightly there were several petitions to Parliament made by the Chartists in that period, each of them attracting huge crowds, made up of hundreds of thousands. One of them took place in 1846, another in 1848. I think on one occasion the Royal Family were evacuated as a precaution. The crowds were generally well-meaning, but perhaps at one of those events the situation boils over somehow...
 
Maybe something along the lines of the Peterloo Massacre takes place at one of those gatherings? That could turn the whole thing violent very quickly.
 
Potato Famine etc happens...and somehow, the Corn Laws STILL don't get repealed. That ought to give you a solidly Tory government and a very angry populace only 2 or 3 years later...?

You can up the odds a little if you go back a bit further...derail Catholic Emancipation, say, or the 1832 electoral reform.
 
This is pretty simple, actually. All you need is one spark and the 10 April 1848 Petition in London, or the Manchester Workhouse Riots, could have gone completely differently. Something as inelaborate as having some random, anonymous, encounter between Chartists protester and London police go slightly different and the whole thing would have exploded; the Chartists would have surged across the Thames, and the military would have intervened. The countryside would go up in flames, and Manchester would likely fall into Chartists hands. Things would quickly have gotten out of control just like they did on the Continent. And that's not even counting what the Irish would do, or throughout the rest of the empire.
 
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