Just been reading a bit about Oliver Cromwell on wiki, plus I watched a documentary on youtube.
Cromwell fought against King Charles the First and the royalists in the 17th century. King Charles lost the civil war and was beheaded in 1649. After this, England was without a monarch and Cromwell became lord protector of the commonwealth. Cromwell died in 1658 and was embalmed and buried in Westminster Abbey.
A few years later the monarchy was restored. In 1661 the new King, Charles the Second, had the bodies of Cromwell and two other Roundheads, John Bradshaw and Henry Ireton, strung up at Tyburn. The heads of the three corpses were hacked off and put on spikes on the end of 20 ft poles, to be displayed at Westminster Hall.
Then in 1685 a violent storm caused the wooden spike that held Cromwell's head to break off from the pole and fall to the ground. An anonymous man, possible a soldier, took it and hid it in his chimney.
The head was exhibited as a curiosity in 1799, having been in the possession of various owners, until it fell into the possession of Josiah Wilkinson in 1814. It stayed in the Wilkinson family until 1960. That same year, Horace Wilkinson handed it over to Sidney Sussex College, Cambridge, where it was finally buried in a private ceremony.
It's quite an amazing, if gruesome, story. Studies were carried out on the head in the 1930s, I believe. The scientists came to a tentative conclusion that the head was indeed Cromwell's because it was apparently embalmed before being removed from the body. Any Tom, Dick or Harry sentenced to be beheaded would not have bee embalmed. The scientists found the embalming to be consistent with 17th century procedures. Finally, details on the mummified head match details on Cromwell's portrait and details on his death mask.
I'm no expert on British history so any corrections welcome.