We finally have it. After all those articles positing lofty questions and then coming back at you with four different answers, we've found a straightforward one. London's oldest museum is... drumroll please... the Tower of London.
The Tower of London — or at least the White Tower within it — dates back to 1078. Built by William the Conqueror as part of his Norman Conquest (duh), The Tower was consequently extended over the next few centuries, with subsequent monarchs making their own mark.
The building took on many purposes; it was a fortification, a prison, the Office of Ordnance, home to the Royal Mint, home to the Royal Menagerie (imagine a zoo in a castle) and perhaps most famously, it's where the Crown Jewels are kept.
All these functions pre-date the Tower acting as a museum, which began accepting members from the public in 1660. Privileged members of the public with special permission had been able to visit before this for a number of years. It's worth noting that 1660 is the same year Charles II was restored to the throne after the English Civil War. We wonder whether allowing visitors was an attempt to show that the monarchy were not so removed (and terrified) of its subjects.
Then, as now, the main attraction was the Crown Jewels. Actually it was more than just regular visitors the jewels attracted, but thieves too. In 1671, the fantastically named Colonel Blood overpowered the elderly Jewel House keeper and nabbed the jewels. Fortunately the Jewel House keeper's son arrived in time to stop Blood and his gang getting away with it — darn those meddling kids — and Blood was arrested and the jewels saved.
Blood somehow escaped his capture and was, rather bizarrely, pardoned by Charles II, but his chance at the jewels was gone. Iron bars replaced the wooden ones surrounding the regalia and visitors were no longer allowed to touch them. Just think: one rotten customer and an incredible experience is stolen from the rest of us for all time.
Even though you can't touch the jewels you can still visit The Tower of London today.