BLAME it on their age - few septuagenarians sell out the Royal Albert Hall these days - their odds-defying longevity in a ruthless industry that routinely chews novelty acts, spits them out and moves on to the next shiny new one-hit wonder, or interviewers' dire lack of imagination but every press junket sees Chas & Dave bombarded with the age-old question: did you ever expect to be up and at it 40 years on?

Without fail, Chas's response is a variation on the same theme.

When he roped in Dave into his next gamble - namely ditching volatile bands without prospects to hit the club scene as a twosome and finally sing in their "own accents about things [they] knew about" - he knew they were in it for the long haul.

That answers that then. Well, not quite.

The forebear of the Rockney genre admits that watching ageing heavyweights conking to the 70s rockers curse - floundering on stage, scrambling to carry a tune or reach their signature high notes - left him pondering where it all went right for the Chas & Dave.

"I knew we'd be together for life," says Dave in his tell-tale Cockney drawl.

"What I didn't realise is that we'd be better in our 70s. My voice is better. I stopped smoking years ago and it probably helped. It's nice to know that some things to improve the older you get. It's a lovely bonus."

Chas & Dave's rags to riches story has been told and retold for decades but genial Chas never tires of a jaunt down memory lane.

The pair first met in 1963. Chas was playing the bass for The Outlaws at the time, and was "thumbing a lift a home" for his now wife Joan one night when a old school friend pulled over. Dave was in the back seat, also hitching a ride.

"I knew Dave for years before we got together. I'd been in bands, had a couple of hit records, but someone would always become disinterested and leave and I just thought, 'I can't carry on like this'. I used to sing in an American accent so I started to write my own songs and sing in my own accent. We got together with Dave I said, 'How about me and you get together?' He was up for it. I knew once we got together, because we were mates, we wouldn't split up," boons the 72-year-old. "We just became ourselves, Chas & Dave."

The band has enjoyed a near uninterrupted career since, except for a brief hiatus following the death of Dave's wife in 2009.

There was one hitch though - they both played the bass. So Chas, who had only just dabbled before, took up the piano in earnest (his pianist mother was rightly elated).

"In the beginning I wasn't interest in the piano," he recalls. "I started off in skiffle group in the 50s. It was great way of getting musicians going - you could bang on anything, send for a cheap guitar. I remember my first gig when I was 13. Someone came up and plonked a £1 note in my hand and I thought this is the life for me.

"Then I heard of this new instrument called a bass guitar; I got one and I was well in demand. In the meantime I had seen Jerry Lee Lewis and I decided I wanted to learn the piano like him. When I toured with him it was a great opportunity to watch him. I always say he taught me but he didn't know he was teaching me."

The duo went on to pen huge chart-topping hits including humorous ditties like Gertcha, Rabbit, The Sideboard Song, and Aint No Pleasing You and were swiftly hailed as the founders of Rockney (Cockney Rock) for their catchy tunes belted out in an unashamed East End lilt. On the back of their growing fame, labels flogged pre-made hits at them but the pair politely declined.

"There are a lot of acts that have recorded songs over the years and they've told me that they never liked them but they did them because they were told they'd be a hit. Then they've got to live with these songs because people want them to sing them. The songs we put out we loved and that's why we still love doing them to this day."

They've remained a constant on the public radar. Although it is fair to say the release of their first studio album in 27 years, That’s What Happens back in 2013, propelled them to legend status, earning the down-to-earth and unassuming "mates" a new generation of young devotees. The Libertines' Pete Doherty has since credited the pair as a huge influence.

Their genre-defining melodies have experienced something a revival and it seems the great British public can't get enough of their unique brand of Rockney. Over the past three years they have performed at Glastonbury, sold out the Royal Albert Hall and closed the Royal Variety Performance.

The release of the record though was as much of a surprise to them as it was to their loyal band of fans.

"The old adage is, 'What comes first? The music or the lyrics? The phone call, that comes first," he chuckles. "We got a call from Warner Bros. The ideas were great, they brought in an America producers. So we did it."

The Royal Albert Hall and gigs for the Queen wrapped up they are Swindon-bound for an "intimate" show at the Wyvern reminiscent of the club spots of the early 70s.

Blending their own original songs with the rock covers of the early days - they found sandwiching their material between well-known anthems was a great way to ease punters into their newfangled style - the setlist, Chas explains, has "grown organically".

"The whole event is virtually the Chas & Dave Story," he enthuses.

With a DVD in the pipeline, endless tour dates, not to mention a new album in the works, Chas & Dave are riding the wave - and as ever they're in it for the long run.

"It's like eating, sleeping and breathing, it's part of my life," says Chas. "It's only work if you wish you were doing something else. That's all I've ever wanted."

Chas & Dave will appear at the Wyvern on Sunday, July 10 at 7.30pm. To book call 01793 524481 or visit swindontheatres.co.uk.