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I'm fairly sure that every time there is large scale civil disobedience or rioting it effects the behaviour of parliament, not necessarily for the better. I imagine that if the miners strike had been entirely peaceful then Thatcher would have had a much harder time sticking to her guns when an entire industry was striking. The Battle of Orgreave (not getting into who started it here) allowed Thatcher to take the moral high ground and helped sway public opinion in her favour.
With regards to the poll tax, yes civil disobedience and peaceful protest as a whole played a much larger part in getting it overturned. However in that instant a much larger percentage of the population were sympathetic to the rioters, and dare I say it a lot more of the people who were sympathetic this time were middle class. This made it much harder for the government carry on regardless.
Riots in and of themselves will not change government policy but they will always have an effect on the behaviour of the government.
Errrr. Poll tax was introduced in Scotland in '89, England and Wales '90.