On 30 January 1649, the political rift in England came to a head — specifically, Charles I's head. This was severed from the rest of the former king's body on a scaffold put up outside Banqueting House, Whitehall — reportedly to a unanimous groan which rose up among onlookers.
Although Charles's execution took place on a Tuesday, it has become tradition (for over 30 years now) to mark the event on the last Sunday of January — this year, 25 January.
Crowds are set to line the Mall (it's free to watch) for a procession of around 500 members of the King’s Army, formed by the English Civil War Society. The procession assembles near St James's Palace at around 11am, then heads through Horse Guards Parade, to Banqueting House for a short wreath-laying service, before parading up Whitehall, through Admiralty Arch, and back along the Mall.
Social media has already picked up on the fact that this year, actual scaffolding has been erected outside Banqueting House, although this would seem to be purely coincidental — and anyway, we're pretty sure the original wasn't put up by people in hi-vis jackets.