An interesting question. Using any of those to create a dictatorship is quite hard, given the checks and balances the country has, but going through them sequentially:
MI5 Coup Against Wilson: Possibly the most plausible if it were to actually happen. Mountbatten would be the Interim Leader but all evidence (the little of it that exists) was that the dreamers who wanted to put this in place wished to replace Wilson and his 'cabal' with moderate blue Labourites and hand over power to a traditional Tory government. Democracy would not be suspended for very long, IIRC. But the coup was so disparate and not ever really considered/planned, so it's quite a weak option here.
The 1981 Riots: Not much chance of them leading to a dictatorship. Thatcher was so unpopular that any attempt to suspend elections with the riots as a justification might simply lead to open rebellion and the police/Army moving against her.
The Miners' Strike: While this period is the most authoritarian Britain has been in recent history, it never got that close to dictatorship. Yes, the Army and Special Forces were deployed against civilians, and movement was restricted around the country for the first time since the war, but the crucial element of the suspension of democracy was absent and, IIRC, never considered. You'd need a fair few butterflies and a lot more violence to make this possible and, again, a leader (eg Thatcher) who was prepared to institute an actual lasting dictatorship, rather than a Roman-style 'temporary government of one'. I don't think Maggie ever really wanted that (apart from in November 1990).
The Poll Tax Riots: See the 1981 riots, really. No logical way for a dictatorship to be established from this.
Others: Short of a government-toppling General Strike in the 1970s and an ensuing Dictatorship of the Proletariat under Jack Jones (which is only seen as likely by the Daily Mail, the addled mind of Baroness Thatcher and morons) it's very difficult to see a single event causing a dictatorship in the birthplace of parliamentary democracy. Certainly between 1960 and 1990. The interwar period has the actual General Strike, of course, which could have gone much worse for the government and maybe seen some degree of dictatorship somewhere along the line. If you read What If Gordon Banks Had Played, one of the great TLs of AH.com, that shows what happens if Enoch Powell leads the Tories to victory in 1974 and the Troubles go a lot worse. That's quite a plausible (if reliant on a much bolder IRA) circumstance for dictatorship in 20th century Britain. And even then it's less of a dictatorship than a dictatorship-by-committee - without spoiling anything, Powell himself is less in charge than those around him.