A VERY, VERY SHORT HISTORY
To understand fully any country's political system, one needs to understand something of its history. This is especially true of the United Kingdom because its history has been very different from most other nations and, as a result, its political system is very different from most other nations too.
Like its (unwritten) constitution, the British state evolved over time. We probably need to start in 1066 when William the Conqueror from Normandy invaded what we now call England, defeated the Anglo-Saxon King Harold and established a Norman dynasty. The Normans were not satisfied with conquering England and, over the next few centuries, tried to conquer Ireland, Wales and Scotland. They succeeded with the first two and failed with the last despite several wars over the centuries.
By one of those ironical twists of history, when Queen Elizabeth of England died in 1603, she was succeeded by her cousin James VI, King of Scots who promptly decamped from Edinburgh and settled in London as King James I of England while keeping his Scots title and running Scotland by remote control. Regal pickings were more lucrative in his southern capital.
A century later the Scottish economic and political elite bankrupted themselves on the Darien Scheme and agreed to a scheme of Union between England and Scotland to make themselves solvent again and so Great Britain with one Parliament based in London came into being. The Irish parliament was abolished in 1801 with Ireland returning members to Westminster and the new political entity was the United Kingdom of Great Britain and Ireland. The southern (Catholic) Irish never reconciled themselves to being ruled by the English and rebelled in 1916 and gained independence in 1922. The northern (Protestant) Irish did not want independence and so the United Kingdom of Great Britain and Northern Ireland arrived. Not a snappy name.
Meanwhile, although the Normans were the last to mount a successful invasion of the country, there were plenty of other plans to conquer the nation, notably the Spanish under King Philip II in 1588, the French under Napoleon in 1803-1805, and the Germans under Hitler in 1940. None succeeeded.
Furthermore, in recent centuries, Britain has not had a revolution of the kind experienced by so many other countries. Some might argue that the English Civil War (1642-1651) was the nation's revolution and - athough it was three and a half centuries ago - it did bring about a major shift in power, 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 colonised in a millennium but rather been the greatest colonisers in history, and in neither of the two world wars were they invaded or occupied.
HOW HISTORY HAS SHAPED THE POLITICAL SYSTEM
The single most important fact in understanding the nature of the British political system is the fundamental continuity of that system. For almost 1,000 year, Britain has not been invaded or occupied as the last successful invasion was in 1066 by the Normans. Is this true of any other country in the world? I can only think of Sweden.
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 this evolution was 1215 when King John was forced to sign the Magna Carta which involved him sharing power with the barons. This is regarded as the first statement of citizen rights in the world - although Hungarians are proud of the Golden Bull of just seven years later.
The so-called Model Parliament was summoned by King Edward I in 1295 and is regarded as the first representative assembly. Unlike the absolute monarchs of other parts of Europe, the King of England required the approval of Parliament to tax his subjects and so, then as now, central to the exercise of power was the ability to raise funds.
The bicameral nature of the British