The single most important fact in understanding the nature of the British political system is the fundamental continuity of that system. Britain has not had a revolution of the kind experienced by so many other countries and Britain has not been invaded or occupied for almost 1,000 years. The last successful invasion was in 1066 by the Normans.
Some might argue that the English Civil War (1642-1651) was the nation's revolution but the main constitutional consequence - the abolition of the monarchy - only lasted 11 years and the Restoration of the Monarchy has so far lasted 350 years (although it is now, of course, a very different monarchy). There was a time in British history which we call the Glorious Revolution (1688) but it was a very English revolution, in the sense that nobody died, if a rather Dutch revolution in that it saw William of Orange take the throne.
So the British have never had anything equivalent to the American Revolution or the French Revolution, they have not been colonized in a millennium but rather been the greatest colonizers in history, and in neither of the two world wars were they invaded or occupied.
This explains why:
• almost uniquely in the world, Britain has no written constitution (the only other such nations are Israel & New Zealand)
• the political system is not neat or logical or always fully democratic or particularly efficient
• change has been very gradual and pragmatic and built on consensus
To simplify British political history very much, it has essentially been a struggle to shift political power and accountability from the all-powerful king - who claimed that he obtained his right to rule from God - to a national parliament that was increasingly representative of ordinary people and accountable to ordinary people. There have been many milestones along this long and troubled road to full democracy.
A key date in