Just how close we came to keeping the monarchy is hard to appreciate today. The Abdication Crisis of 1936-37 could easily have left King Edward VIII "The Last" on the throne, or perhaps his younger brother Prince Albert could have been used as a compromise candidate. As it was, Edward's decision to keep the crown and marry his twice-divorced partner Wallis Simpson appalled the country. The resignation of the entire National Government in protest triggered a general election in November 1936. When Parliament reconvened, the Prime Minister, Stanley Baldwin, in cooperation with new Labour leader Clement Attlee, set about driving Edward out. Massive cuts to the Civil List, the nationalisation of the Crown Estates and the expulsion of Edward from the Church of England appalled many Britons, but overall the public blamed Edward for bringing this crisis to a new high. It was the collapse of the King's Party in Parliament, headed by Winston Churchill, which persuaded Edward that he had to go. In August 1937 he announced that was abdicating.
But events had gone too far to allow the House of Windsor to continue. Edward's last act before departing for France was to sign the Commonwealth Bill into law, which vested the monarch's powers in a Lord Protector. The 1937 Constitutional Convention was Baldwin's lasting gift to the new Commonwealth of Great Britain, creating a President of the Commonwealth, with limited powers of approving bills and dissolving parliament. As an interim, senior Conservative peer Lord Halifax was appointed to the role, with presidential elections scheduled to run alongside the next general election.
This would prove to be much further away than anyone anticipated, with the Second World War delaying it until 1945. But it was the War which made the Presidency the low-key, largely ceremonial post that it is today. The wide differences between Halifax and his wartime Prime Minister, Winston Churchill, persuaded Halifax that his role was largely that of a figurehead.
The first presidential election saw Labour's Ernest Bevin sweep into the job, complimenting Labour's landslide in Parliament. Alongside the sweeping welfare reforms, the 1945-51 Labour government did away with the last vestiges of monarchy, replacing the House of Lords with a proportional representation Senate and overhauling the honours system and the coinage. The British Empire was allowed to slowly fade into the Commonwealth of Nations.
This model of one political party winning the presidency and the House of Commons has continued pretty much ever since, with Harold Wilson's battles with President Willie Whitelaw in March-September 1974 being the notable exception. The selling off of the former royal estates was the big idea of the Thatcher-Tebbit administration in the 1980s, while the Blair-Brown partnership showed how the model could survive even personal enmity.
As for the Windsors, Edward's childless marriage meant that his niece, Princess Elizabeth, became the figurehead of the exiled family from 1972. The family retained a reputation for being fashion trendsetters, with the antics of Charlie Windsor providing a source of much amusement for the British tabloids.
There are still occasional calls for the monarchy to be restored, and speculation has grown following the decision of the PM David Cameron to attend the wedding in April. But President Cable has laughed off these suggestions, saying "A system which produces leaders who can be as different as Stalin or Mr Bean is no system for Britain.