Harry Enfield and Paul Whitehouse on their new TV series Harry and Paul

The comics, who display an appealingly self-mocking view of themselves, joke that in real life they might now be heading for a similar fate. The 49-year-old Enfield laughs: "I recently found out that there are a couple of old people's homes for retired comedians. That's what awaits us."

Putting on the sort of fake elderly voice he used to such effect as one of the Old Gits, Whitehouse chips in: "Sketch shows are a young man's game, and we're so old now. Just to rub it in, the other day I was described by your buddies in the press as 'ageing comedian Paul Whitehouse'. I was grumpy about that description. It may be true, but you don't like to hear it. Despite our great age, Harry and I can still function. We've still got reasonable bladder control."

Whitehouse, 52, adds that he and Enfield are planning a nationwide tour, performing their much-loved cavalcade of characters. "We'd obviously have lots of blood pressure monitors around the theatre. And we'd do loads of sketches as the surgeons with defibrillators all over the stage - just in case. It would be one last hurrah before we send ourselves to that retirement home."

But the truth is, Enfield and Whitehouse are very far from wheeling their Zimmer frames to the nearest sheltered accommodation. As the latest series of their BBC sketch show, Harry And Paul, proves, there's life in the old dogs yet. More than 30 years after meeting in a pub in Hackney, East London, the double act is still crackling with creative energy.

On and off screen, Enfield and Whitehouse send off more sparks than a Catherine wheel on Bonfire Night. At one point during our interview, for instance, Enfield, who has done his fair share of commercials over the years, launches into a mock tirade about his partner's latest TV campaign for a well-known insurance company. "When I've finished work on this series, I'm going to do a bit of yoga.

"I've got no insurance ads coming out - unlike some people who sell their soul to advertisers. I'd never do an ad - out of principle. I'd simply be letting down my fans." Later, Enfield jokes about why he and Whitehouse have collaborated for so long. "Lack of choice. No one else wants to work with me."

The double act's continuing creativity is reflected in the new characters who make their bow on Harry And Paul, which begins on BBC2 on Tuesday. They join such established favourites as the posh surgeons, the snooty shopkeeper, Mr "I Saw You Coming" and the inhabitants of Dragons' Den. The new characters include Gabbatore (Whitehouse), a dodgy foreign prime minister whose true sleaziness is exposed by his decidedly undiplomatic interpreter (Enfield).

In one sketch, Gabbatore tries to bribe the British Prime Minister into buying an aircraft carrier by offering him sexual favours. "I'm sending up a couple of guys, very clean and discreet," Gabbatore tells his British counterpart. "I can get ones that look like Putin and Sarkozy, if you like. Good, we agree. You'll like the aircraft carrier."

Another set of new characters who might acquire the sort of cult status accorded to figures such as Loadsamoney, Stavros and Wayne and Waynetta Slob are "The Benefits". They are a brawling, bawling dysfunctional family, who barge into a local library and try to persuade the head librarian to buy drugs from them.

Enfield, who teamed up with Whitehouse for several series of Harry Enfield's Television Programme and Harry Enfield And Chums in the 90s, explains that The Benefits "are bringing The Slobs up to date. They don't understand anything except their human rights. They're very recognisable characters. There's some social satire in there. They're nice, but hopeless - like a large chunk of Britain."

Whitehouse admits that the pair had to overcome some initial doubts to make the new series, which has been moved from BBC1 to BBC2 despite its predecessor winning a Bafta. "We felt, 'are we outstaying our welcome? Can we top the last series?' But in a way, it would have been more self-indulgent to stop after the success of the last series. So we just pushed on, and as the weeks ticked by, we really got into it."

The characters keep resonating because Enfield and Whitehouse imbue them with rare warmth. "We're not ever nasty," reflects Enfield. "When I watch the comedians on Mock The Week, I think, 'I'm glad we're not like that.' They're so horrible about everyone and, worse, they're really pleased with themselves for being so horrible about everyone.

"Warmth is really important - it makes our characters far more enjoyable to watch. I learnt that early on from doing Wayne and Waynetta with Kathy (Burke]. She invested that slobby character with such a huge amount of warmth that it was five times better than it was on the page."

But the most vital engine that continues to power Harry and Paul is their very durable, symbiotic relationship. "The show endures because we really understand each other," says Whitehouse. "Harry - how can I put it? - doesn't suffer fools gladly. But he's always very indulgent with me. If I come up with a suggestion, he never says, 'No, that's rubbish'. We're very tolerant of each other professionally." A pause. "We hate each other personally, obviously."

Next up for the duo is the possibility of that live tour. "Peter Kay did a 'Mum Wants A Bungalow' Tour," says Whitehouse. "Ours would be the 'Putting Our Mums In A Home' Tour. Would there be an element of Spinal Tap about it? Of course - it would be two ageing dinosaurs on tour. But I think it would be great to see the old characters on stage.

"Harry is now exactly the right age for Mr 'You Don't Want To Do That'. And the Old Gits would be perfect - we wouldn't need any make-up now. Only Kevin and Perry would tricky now."

The duo are not ruling out another series of Harry And Paul either. "We still get the same buzz as ever out of working together," says Enfield. "Yesterday, we were helping out a friend Jason Lewis with a BBC3 pilot. For one sketch, Paul and I were dressed as policemen and we didn't concentrate for a minute. Poor Jason was trying to do 20 sketches in a day, and Paul and I were just mucking about. He couldn't keep control of these two sad old men."

Whitehouse closes by agreeing that the thrill of "mucking about" has definitely not waned. "You do feel as you get older that this is an undignified way to make a living. But, there again, we love it and feel very fortunate still to be doing it. As my kids say to me, 'Is that your job? You're so lucky.'"

As Smashie and Nicey would put it: You ain't seen nothing yet.

Harry And Paul, BBC2, Tuesday, 9.30pm

• This article was first published in the Scotland on Sunday on September 26, 2010