4 February 1975. Most people expected Edward Heath to win the Conservative Party leadership contest. If he had, not only Britain but the world would be different because privatisation and monetarism would remain entirely theoretical at least until the collapse of the Soviet Union.
30 August 1918. After the dismissal of Police Captain Theil for union activities, the National Union of Police and Prison Officers demanded a pay increase and increased War Bonuses as well as recognition of the Union. They gave a deadline of midnight on 29 August for a settlement. No settlement was forthcoming and on 30 August they struck. On 31 August, the government gave in to all demands apart from recognition. But suppose that strike had become the start of a general strike... and a revolution?
10 February 1763. The treaty of Paris gave Canada to Britain while returning Saint Domingue, Martinique and Guadeloupe to France. Suppose it had been the other way around. American revolutionaries acknowledged that had France still been a power in North America, there would have been no American Revolution. Suppose Canada had remained French and the thirteen colonies British?
24 March 1603. Under the terms of Henry VIII's will, if his children had no issue, then next in line should be the descendants of his sister, Mary Tudor. If this had been followed, Queen Elizabeth I's successor would have been Lady Anne Stanley and she would have been followed by the Strange dynasty. The Barons of Strange did not share the Stuarts' belief in the Divine Right of KIngs... and perhaps there might have been no English Civil War.
663-4 AD The Synod of Whitby decided that Britain would follow the Roman rather than the Celtic form of Christianity. Toynbee has suggested that this was the end of a nascent "Far Western Christian" civilisation. Imagine if it had been the other way and Britain sent missionaries to pagan Scandinavia, and perhaps after the Islamic conquest to Iberia and beyond, to North Africa?