The postman's approach to Sir David Attenborough's home on Wednesday might have been worthy of one of the great naturalist's hushed TV commentaries.

There he was, laden down with hundreds of cards, letters and gifts – for Sir David turns 100 today.

In fact, the postie needed crates to manage the massive haul of mail and carry it to the broadcaster's home in Richmond, south-west London.

And then there was another... this time laden with parcels.

National treasure Sir David said he felt overwhelmed at the outpouring of affection in an audio message yesterday.

'I had rather thought I would celebrate my 100th birthday quietly, but it seems that many of you have had other ideas,' he said. 

'I have been completely overwhelmed by birthday greetings, from pre-school groups to care home residents, and countless individuals and families of all ages.

'I simply can't reply to each of you separately, but I'd like to thank you all most sincerely for your kind messages, and wish those of you who have planned your own local events: Have a very happy day.' 

The naturalist – born in the year of the General Strike and only eight years after the end of the First World War – joined the BBC as a trainee producer in 1952 and first appeared on our screens more than 70 years ago.

He has been controller of BBC1 and BBC2, overseen the launch of colour television, and even turned down the role of director-general. 

He has since won dozens of awards for his documentaries, and last year became the oldest Daytime Emmy winner.

Events are being held up and down the country to mark Sir David's birthday, including a star-studded live BBC event at the Royal Albert Hall, hosted by Kirsty Young and with appearances by Sir Michael Palin, Steve Backshall, and Chris Packham.

The event will feature dramatic wildlife stories, accompanied by live music from his programmes by the BBC Concert Orchestra, alongside spoken reflections from public figures and leading advocates for the natural world.

The corporation will also mark the broadcasting icon's 'extraordinary milestone' by broadcasting a mix of new and old series by the legendary natural historian.

Elsewhere, the free flower festival Chelsea in Bloom in London returns from May 18 to 24 with a theme of 'out of this world', incorporating a floral celebration for Sir David's birthday.

And at the National History Museum, an immersive experience features footage projected on to the walls with Sir David's voice playing in the background.

Reflecting on his life a few months before his birthday, Sir David candidly said he was not so much afraid of death but of 'not living enough'.

Sharing his acquired wisdom, Sir David added: 'After living for nearly a hundred years on this planet, I now understand that the most important place on Earth is not on land but at sea.

'If we save the sea, we save our world. After a lifetime of filming our planet, I'm sure nothing is more important.'

In December last year a letter was unearthed that showed how things could have been very different for Sir David – and British TV.

The correspondence, from July 1952, reveals the haphazard way in which his seven-decade career at the BBC began.

After he applied to become a producer, the BBC turned him down – but encouraged him to apply for its training scheme, prompting him to have another go. The letter tells the 26-year-old his interview was a success, adding: 'I am now writing to let you know that you were selected for the Television Training Course as Talks Producer.'

The BBC said that the success of his second application 'arguably changed the course of broadcasting history'.