"I don't want to sound like an old git," he says, before continuing with a phrase that immediately quashes this intention, "but I am disappointed by aspects of contemporary youth. The current generation of teenagers is way, way too passive. They don't believe they can empower themselves, and as punks that's what we did. We said, 'No, we don't want this (society] and we're going to shout about it.' That attitude is a healthy one. To continually question established thought is the only way to change it. I absorbed that ethos and it hasn't changed to this day – I do not take no for an answer."
But what did a middle-class boy from England's Home Counties, indulged by his parents in his passion for bird-spotting and fishing – a Durrell-esque existence, by the sound of it – find to get so angry about? Apparently the years that the young Packham spent grubbing about in the Hampshire soil for insects, examining plant life and discovering badger setts, did not render him oblivious to the turbulence of society beyond the garden gate.
"In 1977 Britain wasn't a happy place – we passed from the economic troubles of the early 1970s straight into Thatcherism; it was a difficult time for a lot of people, including me. That whole punk movement suited my mental state. I was antisocial and I deliberately made myself into a freak so that no-one would come near me," he laughs.
"Punk, for me, was about saving up to buy a second-hand guitar, making music in the garage, playing gigs in pubs. It wasn't like X Factor, going on TV to become famous. Punk was the antithesis of that."
And, in some ways, Packham – who had more of a touch of Billy Idol about him when he first appeared with a bleached barnet on The Really Wild Show in the 1980s – is the antithesis of traditional TV wildlife experts. Having taken over from bearded Bill Oddie on Springwatch earlier this year, he described himself as "probably the only clean-shaven man in ornithology".
He also attracted ire and admiration in similar measure for weaving titles of songs by The Smiths into his commentary. Last month he provoked shrieking when he opined that, if we really are a nation of animal lovers, then the money we pour into panda conservation might be better spent on endangered species in Britain.
Having acquired the rather harsh sobriquet of 'panda killer', Packham apologised for any misunderstanding caused. "I love pandas," he stated. "I love all cuddly animals." In his second season at the helm, however, Packham seems to have been embraced by viewers as warmly as a newborn duckling. It is undoubtedly due in part to the chemistry that exists between him and fellow presenter Kate Humble.
If Autumnwatch were a Hollywood movie, Tom Hanks and Meg Ryan would surely be cast as Packham and Humble – he with his dry and manly sardonic charm; she with her uncontrollable blonde curls and the wide-eyed effervescence which makes it impossible for any man not to melt in her presence. Viewing figures hover around four million in the primetime Friday slot. North of the Border, that figure is likely to rocket when Packham and the team arrive in Scotland in November. It's a trip to which he's very much looking forward. "I've spent a lot of time in Scotland – it has some of the sexiest wildlife in the UK. The Scottish wildcat is undoubtedly one of the most difficult species of all to see, and I honestly don't think I've ever seen a true one, despite hours of watching. Then there's the pine marten – beautiful, beautiful animal – the capercaillie, golden eagle, osprey, otters, red squirrels – I could go on.' And he does. "About 20 years ago I spent an entire winter living in a cottage near Inverness," he gushes, "I thought it was wonderful." What, even in the dark and cold? "Well, I read a lot of books and drank a lot of whisky," he admits. "Probably too much whisky, in fact – I can't touch it any more."
But the wildlife still intoxicates him. "Scotland's a magnet for naturalists. I was first taken there by my parents as a kid, because I was really into trout fishing at the time. But then when I was 18 and my girlfriend got her first car – a Mini – we drove all the way up to Scotland and slept in it beside Loch Leven, eating cans of beans." (I can't help thinking the girl must have been pretty smitten to bed down in a small car with a grown man subsisting on Heinz's finest.)
"We drove up more often in summer and spent a lot of time exploring the Outer Hebrides in particular. And I remember being at the top of Cairn Gorm for the first time, that was fantastic. As a nation, you (Scots] are spoilt for wildlife.'"
It's to Cairn Gorm he'll return with Autumnwatch for four days of filming, to be edited and broadcast in the same week. This means long, action-packed days for the presenters, as you'll know if you saw Packham and Humble filmed at 6am on a vast Norfolk beach last week, beneath a glorious apricot sky, relishing the extremely rare sight of a flock of knot swooping, with the elegant velocity of a thousand tiny fighter jets, across the mudflats.
When he's not filming, or photographing wildlife in far-flung destinations, Packham divides his time between south-western France, where he owns a house, and the New Forest, where he rents one in order to stay close to where his 14-year-old daughter lives.
Does he ever switch off? He reads for pleasure every night – but fiction rather than wildlife books, he says, because that puts him back in the realm of work and the Sisyphean task of discovering all there is to know about the constantly evolving natural world. The zoology graduate and vice-president of the RSPB also finds pleasure in archaeology, and may be found exploring Scotland's ancient castles. "There's a lot of romance in them, not least because they're in such beautiful settings. The ruins of Urquhart Castle by Loch Ness; smaller castles in Speyside."
It's all a far cry from his punk-rock years, but for Packham the transition from disaffected youth to independent adult was made with eyes wide open. "I saw a young woman on TV recently, complaining, 'I got my A levels, I've got my degree – and now I haven't got a job.' It made me laugh because I was on the dole for two years after university and in the end I had to go out and invent a job for myself." Photography was his starting point in a wildlife career that has spanned three decades. "I sold my music gear because I wasn't getting anywhere with that – starting a band with your mates is only a way to guarantee that you all end up hating each other, anyway – then I bought a camera and a rusty Renault 16 that cost 300 and drove to the south of France.
"I slept in it there for six weeks and started the process of teaching myself to take photographs. After that, I came home and was on the dole, using that money to buy petrol and film. I drove around the UK's nature reserves, sleeping in their car parks and getting up at dawn every morning to take photographs. "I sold my first photograph – of an owl – to Gamekeeper & Countryside magazine. And it was on the cover," he recalls with a hint of pride. "So I thought 'right, I can do this' and I went on to get the next one, and the next."
Asked whether he has a preference for spring or autumn when it comes to observing wildlife, Packham has a metaphor which, if not quite Keatsian in its celebration of the seasons, is poetic in its own way. "It's like the difference between drinking beer and brandy.
"Spring is a great slurp of instant, refreshing relief, because you've waited all winter and suddenly everything flows in a very short space of time, singing and flowering. Autumn, on the other hand, is a glass of brandy, something to savour. There's all the energy and dynamism we see in spring, but it happens over a longer period of time."
Is there a time of year that he doesn't enjoy? "August," he says, flatly. "It's pretty dead, not much going on. There's a few butterflies and blackberries, but really it's just a lull."
But is not a lull a beautiful thing, a time for peace and reflection and…
"Naah, I don't like that," he briskly interjects. "I haven't got time for a lull in my own life, let alone in the natural world! There's got to be action."
A perfect excuse for Packham to spend a month at the Edinburgh Fringe, perhaps? "Or painting my house," he responds, ever the pragmatist. "That's my only artistic pursuit in August. I can do art with a roller and a can of emulsion – I'm a real Jackson Pollock."