The digital switchover means that from now on, viewers will need to use Freeview, satellite or cable.
An estimated 12 million television sets are affected in the London area, but most homes have already switched over.
The process to turn off the transmitter, which is being managed by communications infrastructure firm Arqiva, began at midnight, when BBC director general Mark Thompson turned off the switch.
Light show at Crystal Palace
Next month, every single old fashioned television in the London area will stop receiving a TV signal as the main broadcast tower at Crystal Palace switches to digital only broadcasts.
Signals sent in easily decoded waves will be replaced by a stream of digital bits and bytes that only a complex computer algorithm can understand. Digital squeezes more channels into the same space, but aliens listening for signs of intelligent life will see hints of regular radio patterns being replaced with random gibberish.
Digital also means less radio spectrum required for broadcasting TV signals, and more for them to flog off to the mobile networks, so they can use the bandwidth to deliver YouTube videos to mobile phones.
A press release – which I would ordinarily delete, but was actually written sensibly for once announces a GRAND EVENT to mark the switchover.