But the anniversary always used to be given as 10th January instead. Saturday 10th January 1863 was the day the railway opened to the public, and that's the day that's always been quoted everywhere as Day One. Friday 9th January was more Day Zero, the day the directors took a one-way ride on their new railway and celebrated with a slap-up banquet. No, the proper anniversary's surely, definitely, 10th January. And, contrarily, TfL agree.
This is from the official list of TfL milestones...
That's right, in 2007 TfL published hundreds of thousands of tube maps with an artwork on the cover declaring that on 9th January 1863 the Underground hadn't yet started. Now they've changed their mind and say that 9th January 1863 is The First Day after all. How strange.
Oliver Green from the London Transport Museum, who ought to know what's what, is giving a free lecture at Gresham College on the 9th January which he's advertising as the actual day.
Meanwhile the Royal Mail are bringing out some rather lovely anniversary stamps on Wednesday 9th, like so.
But staff in the control room at Farringdon station seem sure it's the 10th. Maybe they missed the internal email.
And here's a plaque outside Baker Street station, bolted to the wall in front of the taxi rank, unveiled for the Underground's centenary in 1963. Surely this is convincing proof that January 10th is the definitive opening date... or was.
It seems that at some point in the last fifty years, more likely in the last five, someone at TfL has decided to switch the official Underground anniversary from the 10th of January to the 9th. A deliberate decision, an approved choice, a rolling back to the day before. And I wonder why.
Clearly there are two possible anniversaries for the birth of the London Underground. One's the day passengers were first allowed on board in their thousands, which is the day I'd pick as the launch date. And the other's the day the directors rode alone, which might technically be the start, but somehow feels wrong. How telling, and how sad, that TfL has shifted from the public to the private.
So when the anniversary trumpet sounds next Wednesday 9th, do raise a glass for one of the finest innovations London ever saw. But raise a bigger glass on Thursday 10th, the true 150th anniversary of the day Londoners began to travel beneath the capital, and never looked back. Let's celebrate...
What's on this weekend? Spring Into Summer Saturday 30 & Sunday 31 May
40 free guided London walks. Purley Festival Friday 29 - Sunday 5 June
Bunting week, below Croydon. E17 Art Trail Sat 30th May - Sun 14th June
250 arty Walthamstow things.