Below, we've started a list of commonly mentioned London places that don't exist. Some are genuinely non-existent. Others are places we know by nicknames that differ from their official names. Feel free to suggest additions in the comments.
Big Ben: The most famous clock tower in the world. Ah, but "It's the name of the bell not the tower". So says every pedant ever. Even pre-school shows like Peppa Pig and Go Jetters have pointed this one out. If we want to get really pedantic, though, then it's not the bell, but the largest of five bells, and it's official name is The Great Bell of Westminster and not Big Ben (just a nickname). The tower is, of course, now the Elizabeth Tower. It was never St Stephen's Tower, as commonly believed. See here for why we're still calling it Big Ben.
Bond Street: There's an Old Bond Street and a New Bond Street, and a Bond Street station, but nowhere other than the Monopoly board can you find plain old Bond Street. (Well, not in central London, anyhow. There are Bond Streets in Chiswick, Ealing and Forest Gate, but not in central London.) Find out why, here.
Elephant and Castle roundabout: It doesn't have one. Not any more. If you don't believe us, go check.
London: It's not easy to find a place called London. There's Greater London, Inner London, Outer London and the City of London, but can we find any place that bares the official name of just 'London'. Why yes, it is a European Parliament constituency. An unfortunate side-effect of our withdrawal from the EU — which it seems only we have noticed — is that London will cease to exist.
Millennium Bridge: Officially, it's the London Millennium Footbridge. That's too wordy, and shares an abbreviation with Lazy Mother F*cker, so everyone calls it the Millennium Bridge. Except for those of us who were here when the crossing first opened. We all call it the wobbly bridge.
Millennium Dome: It's the name that still trips off the tongue for many of us. That, or simply just 'the Dome'. But the official title of this Greenwich landmark has been The O2 since 2005. One exception. During the 2012 Summer Olympics and Paralympics, the dome was used as a sports venue. It had to drop its sponsor name as part of the deal, and so became the plain old North Greenwich Arena for a few weeks.
Old Bailey: Another nickname. Its official title is The Central Criminal Court of England and Wales.
Petticoat Lane: The East End market has traded on land east of Bishopsgate since time immemorial. The main thoroughfare through the market was known as Petticoat Lane until around 1830, when it was changed to its present name of Middlesex Street. A newspaper commentator in 1845 noted 'Although Middlesex Street is painted on the walls on each side of the lane, 'Petticoat Lane' it is still called and is likely ever to be so.' Eight generations later, and he hasn't been proved wrong. More here.
Post Office Tower: You can tell a person's age by how they describe the massive telecoms tower in Fitzrovia. Under 40, and they'll probably call it the BT Tower — it's modern official name. Older Londoners will plump for the Telecom Tower or Post Office Tower or even the GPO Tower. These are all crap names. It's about time that the tallest building in the West End got a proper epithet. We're proposing the Low Tower. It's deliciously self-contradictory, but also remembers Archibald Low, the forgotten pioneer of TV (and drones, and Strictly Come Dancing).
St Pancreas: Obviously, it's St Pancras.
The Strand: Because, technically, it's just Strand. Only weirdos like us insist on pointing this out.
Tower of London: So it is known to just about everyone. Yet the stronghold's official name is Her Majesty's Royal Palace and Fortress of the Tower of London. And they're yeoman warders, not beefeaters!
Westminster Abbey: This great ecclesiastical building is formally known as the Collegiate Church of St Peter at Westminster. That's because it's not an abbey. England hasn't had abbeys since Henry VIII gobbled them all up nearly 500 years ago. Come to think of it, the name Westminster Abbey is also tautological. The 'Westminster' bit is a reference to the 'minster to the west of London'... that is, Westminster Abbey.