Broadcasting legend Attenborough pressed the red button to illuminate the 219-metre high transmitter tower in Crystal Palace, sending out beams of light across London. The tower serves around 5m homes across the capital and the surrounding counties with TV pictures.
He was joined by various celebrities, including TV personality Professor Brian Cox, BBC Radio 2 DJ Chris Evans and programme maker Sir Peter Bazalgette, for a special ceremony under the transmitter, owned by Arqiva, the company that runs the UK's transmission architecture.
At midnight on April 18, BBC director general Mark Thompson attended the transmitter station to see analogue BBC One, ITV1, Channel 4 and Channel 5 switched off, in a significant step forward in the £630m digital switchover project. Analogue BBC Two had been turned off on April 4.
> London bids farewell to analogue TV - feature
The guests recalled their most cherished TV memories, including Attenborough discussing the iconic moment when man walked on the moon. Professor Brian Cox said he also treasured the touchdown of the Apollo 13 landing craft.
"TV that's watched by millions of people, so significant fractions such as 10 or 20% of the population, is overwhelming important," said Cox, referring to the fact that 18% of UK TV coverage is served by Crystal Palace and its relays.
"The argument that's often made is that in a digital world, with the internet, you can just choose what you want to watch. But I don't think that's genuine choice really. I think that the foundation of choice is that you see things that you wouldn't normally have watched."
Former Playschool presenter Floella Benjamin recalled the time her stage show in the West End was halted because tennis legend Arthur Ashe was on the brink of beating Jimmy Connors in a momentous sporting moment.
Ex-BBC director general Greg Dyke shared his precious TV moment of Geoff Hurst's goal in the 1966 World Cup, and said his favourite comedy was The Likely Lads.
"This is a momentous moment in terms of choice of TV," said Dyke, discussing the London switchover. "We are all guilty of forgetting the range and quality of television we have in this country and it's all got a lot better with the digital switchover."
Over the past five years, Arqiva has installed new digital equipment at over 50 TV transmission sites across London and the Home Counties, from St Albans to Dorking, enabling the switch to high power Freeview signals.
The digital switchover will reach completion on October 24 when analogue TV disappears forever in Northern Ireland.
Arqiva chief executive John Cresswell said: "This is a broadcasting landmark and digital switchover is an amazing engineering and technical feat and a fantastic story of British success.
"The UK has an amazing record of producing fantastic television. Freeview is the platform of choice across the UK and the investment we have just made will ensure it continues to be relevant for the next 20 years."
Alongside the shift to digital TV, the switchover has also cleared London's airwaves for the delivery of next-generation 4G mobile broadband services in the future. Ofcom will run an auction of the freed-up spectrum later in the year to allow mobile firms to start offering 4G to consumers.
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Watch a video of the Crystal Palace switchover event below: