The songs remain the same...

Why are The Rolling Stones still playing rhythm and blues after almost 50 years, when The Beatles managed to change their tune entirely in just seven?

Why is Noel Gallagher still belting out bolshy Britpop while Damon Albarn composes Chinese operas? Why, when some bands change, do others sound the same, again and again?

In 1991, as Oasis were coming together for the first time in a back room in Burnage, The Levellers released Levelling the Land, their second and still most successful album. Play it alongside their latest LP, Letters from the Underground – released in this, their 20th-anniversary year – and you'll find the similarities are legion. The band's feisty folk-punk has trained its sights on a variety of political targets over the years – globalisation, civil liberties, the Criminal Justice Act – but the template remains the same.

The only time The Levellers tried something new, on 2000's cerebral, drug-influenced Hello Pig, they found their sales dipping drastically and their deal with Warners quietly curtailed. Their fans knew what they liked, and they liked what they knew. Indeed, their disapproval was so powerful and public that the band felt compelled to apologise and go back to doing what they were doing before. Theirs is a limited but loyal following, and taking liberties with the fans' expectations proved to be a dangerous business.

It's been more than 10 years since the release of Ash's first LP, 1977, yet Tim Wheeler's tuneful teen-punk combo are returning to The Roundhouse tonight to play their debut in its entirety. It won't be a massive musical stretch for the band – their current, mature-ish sound is still reassuringly familiar to those who first heard and fell in love with Ash a decade ago.

However, a live performance of 1977 will keep those nostalgic fans happy and, after all, concerts are costly. If everyone knows the running order in advance, and has some emotional involvement with it – memories of teen romance, say – then it removes the ever-present risk of buying an expensive ticket, only to find the show full of new and unfamiliar material. The same principles apply to an album release. Many fans want to browse the iTunes store safe in the knowledge that their favourite acts will stay true to their core appeal.

Creative evolution is a luxury. Only acts that achieve longevity have the opportunity to grow and change, and even then they must be brave enough to risk alienating their fans, losing their record deals or producing something that exposes their limitations rather than their capacity for boundless invention. Radiohead, Blur or Pink Floyd are rare beasts. Sometimes, bands who took an adventurous turn somewhere down the road find themselves reaching a creative cul-de-sac and going back to basics to shore up sales and reassure their loyal fans. U2, for example, returned from Pop and Zooropa's dance tropes to the stripped-down rock that first made them famous.

Their contemporaries Echo and the Bunnymen are another case in point. But for a four-year hiatus in the early Nineties, the Liverpool post-punks have been ploughing the same musical furrow for three decades. Their 11th album, The Fountain, is due later this year. While they continue to receive almost uninterrupted praise from critics and fans (including Coldplay's Chris Martin, who has covered their songs live and appears on The Fountain), there's no particular incentive to break their own mould. And perhaps, if they did, they would only demonstrate a disappointing lack of range. The list of inadvisable sonic experiments is long, and no band would wish to add to it with a poorly judged change of direction.

Stiff Little Fingers formed in Belfast in 1977, soon after punk's Year Zero. Thirty years later, frontman Jake Burns and bassist Ali McMordie are the only remaining members of the original line-up, but their re-tailored outfit still adheres to its original punk template. While the Troubles, which filled his lyric sheets in the early days, may be over, Burns has plenty of new preoccupations to turn his pen to – including the conflict in Iraq.

Yet while he says he'd love to have developed a career with the diversity of Dylan, Burns admits that he'd have failed in the attempt. Their few forays into the unknown territory of brass arrangements and electronics have merely irritated Stiff Little Fingers' fans. Their next (now delayed) album promises more of the same crunching trad-punk.

As does Guerilla Tactics, the latest record from The Alarm, a band who, unlike Stiff Little Fingers, never even thought to change. Frontman Mike Peters is the sole remaining member of the original group, but resurrected the name in 2001 after a 10-year break, with an all-new line-up. The Alarm once toured with U2 (and Dylan), but while his peers evolved, Peters remained content to channel Joe Strummer on every record, indulging his nostalgic urges and staying true to the punk rock that first got him excited about music. Peters pleases himself, others please their fans, and still more are merely aware of the limits of their creativity.

And many more youthful acts show signs of going the same way as their forebears. The Charlatans have steered a similar course for almost two decades, changing tack only slightly along the way to embrace the occasional new dance-music influence. The chunky guitars and organ chord-bashing that have always defined their sound are still present on their latest, download-only album, You Cross My Path. Tim Burgess, the band's lead singer, has taken to singing what is still their signature hit, 1990's "The Only One I Know", on-stage with Mark Ronson, who covered the track for his album Version. It goes to show how closely The Charlatans have followed the formula that first brought them success.

The Verve, meanwhile, are becoming known as the band that consistently break up and then re-form again. Their brand new (fourth) album, Forth – currently top of the album charts – has the same combination of Richard Ashcroft's vocals and Nick McCabe's tortured guitar lines that frequently made them great in the first place. Unfortunately, it also contains much of the same psychedelic noodling that sometimes had listeners of Urban Hymns and A Northern Soul reaching for the skip button.

Think, too, of all those heavy-metal acts from both sides of the pond, whose genre is entirely unapologetic about its fixed traditions. Iron Maiden, 33 years and 80 million album sales after their formation, just keep on rocking. Music critics seem to have perpetuated a myth that music must evolve to remain vital – but what's wrong with a band staying true to their roots? Change is a big risk. If your fans don't like what they hear, they won't buy it, and no number of five-star reviews is going to impress a record company whose main concern is the bottom line.

And look again at the bands that started it all, whose musical adventures inspired many of the aforementioned acts. The Beatles' career is often held up as a paradigm of pop evolution. But what about their contemporaries, the still-kicking Stones? Their rhythm-and-blues template has shifted funkward for a while, or swerved occasionally into a country lane, but in a 46-year career, Mick and Keith have rarely fiddled with the fundamentals. Why would they? If it ain't broke...

The Charlatans

Years: 18; Albums: 10

The Charlatans' first hit single, 1990's "The Only One I Know", set the tone for a career of jangly indie with signature keyboard-bashing. A couple of their albums have contained the requisite dance influences, but their foundations are immovable. Their latest album, You Cross My Path, could have been made in 1991.

The Levellers

Years: 20; Albums: 13

But for one album, on which they explored an ill-advised new direction, 'anarcho-crusty' folk-punks The Levellers have stuck to their guns for 20 years. While the political preoccupations that pepper their lyrics have changed with the times, their sound has not.

The Verve

Years: 19; Albums: Four

Singer Richard Ashcroft and guitarist Nick McCabe have only suffered each other's company long enough to produce four albums in nearly two decades, but they all sound pretty much the same. Urban Hymns had the highest quotient of radio-friendly tunes, hence its success. But each of the four contains anthems and noodles in almost equal measure.

The Alarm

Years: 27; Albums: 11

Welsh punk perennials who still worship The Clash, The Alarm have just produced their third album since re-forming. The line-up has changed, but spiky-haired singer-guitarist Mike Peters remains at the helm.

Stiff Little Fingers

Years: 31; Albums: Nine

A Belfast-based punk act first inspired by The Sex Pistols and the Troubles, Stiff Little Fingers recently played at the Meltdown Festival in London, but their promised new album has been delayed due to – shock horror! – a change of direction...

There have been country-tinged albums (like bits of Beggars Banquet) and dance-ish albums (like Black and Blue), but to all intents and purposes, The Rolling Stones have remained a rhythm and blues group to their core.