"Do me a favour, I'd have to put my trousers on!" exclaims Sir David Attenborough when I call him to chat about his new book, Life in Cold Blood.

This is the humorous response from the broadcasting legend when I mistakenly tell him he is due in Borders Bookshop in Oxford for a signing session in a few hours' time.

A quick check on my diary reveals that Sir David is actually coming to Borders on Wednesday, from 4.30pm to 5.30pm.

But the acclaimed naturalist has such an affable manner that he leaves me feeling quite happy about getting off to a false start.

Now in his early 80s, Sir David has been the enduring voice of natural history programmes for the past 50 years.

And although Life in Cold Blood, now showing on BBC1, is to be his last major series - it focuses on reptiles and amphibians - Sir David tells me his work is not finished yet.

"I'm working on a series about Charles Darwin and evolution - I'm still writing it at the moment and I expect it to be screened next year because it's Darwin's bicentenary next year."

Does he think of the nine different Life series he has made in conjunction with the BBC Natural History Unit as an incredible achievement?

Sir David replies modestly that he never set out to capture all the elements of evolutionary history, and stresses that what viewers are attracted to in the programmes he makes is not him - it's the fascinating creatures he is focusing on.

"I am definitely second billing," he insists, and adds that he still gets a thrill from making a new discovery.

"During the making of Life In Cold Blood I was absolutely delighted to find a dwarf chameleon the size of a fingernail," he said.

"I was looking for it in Madagascar in 1960 and never found it, so I was very pleased.

"There are extraordinary things all around us - these programmes are not in the least about me."

Although Sir David is a Cambridge graduate, he tells me he enjoys visiting Oxford and has strong connections with the city.

The father-of-two, who is the younger brother of director and actor Richard Attenborough, is a Patron of the Pitt Rivers Museum in Parks Road.

His son Robert, who now lives in Australia, was a student at Oxford University, and Sir David also visits Oxford from time to time to drop in on his old friend, the zoologist Desmond Morris.

"Desmond and I have known each other for a long time," he said.

Sir David is now touring a number of bookshops to promote Life In Cold Blood, the book accompanying the latest series.

Are customers who queue up at the signings pleased to see him? "People must be delighted to see me otherwise they wouldn't turn up," admits Sir David, but once again he seems determined to be modest and play down his popularity.

Sir David is signing copies of Life in Cold Blood at Borders on Wednesday, from 4.30pm.