When the brand plays on...

If you'd walked past the 100 Club in London's Oxford Street earlier this month and heard the chords to the new-wave anthems "Mary of the Fourth Form" or "Rat Trap" ring out, you might have thought Sir Bob Geldof had finally realised his solo career was going nowhere and decided to reform the Boomtown Rats for one last hurrah. In fact, Sir Bob was nowhere to be seen. Indeed, even if Rats guitarist Gerry Cott was in the audience, the bassist, Pete Briquette, and piano-player Johnnie Fingers, he of the stripey pyjamas, and the second most identifiable member of the Irish group were not in attendance.

The Rats – Geldof insisted they drop the Boomtown bit – featured just two of the originals, guitarist Garry Roberts and drummer Simon Crowe. "Reforming the band had never really been on the cards, but somehow here it is," says Crowe. "Garry and I said: 'if we are going to do it some time, then why not now? It's our music. So why should we not play it in whatever way we want?" Even minus Geldof? But it seems the four-piece Rats already have more dates up lined up for 2009. And they're only the tip of the iceberg of heritage bands currently doing the rounds.

A fortnight ago, I went to see Chicago at ExCel in London, as part of the British Motor Show Music Festival. More fool me, you might think, but I've always had a soft spot for the American group who put the horns centre stage with their first three multi-million selling albums, all doubles, before the 1976 transatlantic chart-topper "If You Leave Me Now" waylaid their career into soft-rock mush. Bassist Jason Scheff sang that one since Peter Cetera, the song's originator, left the band in the Eighties.

On closer inspection, if founder members Robert Lamm (keyboards, vocals) and Lee Loughnane (trumpet) were present and correct, James Pankow (trombone) and Walter Parazaider (saxophone), the other two originals in the eight-strong personnel, had stayed home in the US, their places taken by deps Nick Lane and Ray Herrmann. You would have thought that, for their first European tour in 18 years, Chicago would have pulled out all the stops for their fans, some of whom had travelled great distances.

The Rats and Chicago are only one of many with a less than full complement of originals. I also recently chanced upon the British group Ten Years After playing a free concert in Switzerland. Woodstock veterans Leo Lyons (bass), Chick Churchill (keyboards) and Ric Lee (drummer) all looked their years but Alvin Lee (no relation), to all intents and purposes the voice and virtuoso guitar of "I'm Going Home" and "Love Like a Man", the original frontman and primary songwriter, was nowhere to be seen. Joe Gooch, his 31-year-old replacement since 2003, did a fine job, but I still felt a bit cheated. The classic line-up briefly reunited in the late Eighties, yet, according to Lyons, "it was obvious Alvin didn't enjoy playing with us any more. Ric, Chick and myself, we love playing as a band. And the fans wanted to see Ten Years After in concert. Joe was a lucky find, he's a brilliant guitarist."

Similarly, with From The Jam, drummer Rick Buckler and bassist Bruce Foxton, have tapped into a fortysomething audience of mods eager to hear the Jam material Paul Weller has mostly ignored for 25 years. Two sell-out tours later, they're laughing all the way to the bank.

Supply and demand is the governing principle behind the band as a brand. Earth, Wind & Fire and the Beach Boys, who have often toured the US with Chicago, feature only two members people would recognise. EWF bassist Verdine White leads the funk outfit, aided and abetted by falsetto vocalist Philip Bailey, who arrived in 1972. Beach Boy Mike Love joined his cousins Brian, Dennis and Carl Wilson in 1961, and is still singing "Fun, Fun, Fun", with Bruce Johnston, a member of the band between 1965 and 1972 who returned at the end of 1978. Carl and Dennis Wilson died a long time ago, ending any hopes of re-forming the classic line-up.

Yet, neither ill health nor the grim reaper seem to be able to stop an act with a ready-made audience. The Who will tour the US in October minus the late Keith Moon and John Entwistle, but very much The Who as long as Roger Daltrey twirls his microphone lead and Pete Townshend windmills his guitar. Hard rockers Uriah Heep are on in Europe and Russia, with guitarist Mick Box at the helm, the deaths of bassist Gary Thain and vocalist David Byron, and the departure of organist Ken Hensley, just distant memories. And it's still the same old song for the Four Tops, with Abdul "Duke" Fakir surrounded by Ronnie McNeir, Theo Peoples and Roquel Payton, Lawrence Payton's son. Last year, guitarists Scott Gorham and John Sykes were back in town with Thin Lizzy, paying tribute to the late Phil Lynott. Organist Ray Manzarek and guitarist Robby Krieger, who made two albums as The Doors after Jim Morrison's death in 1971, have attempted to reform the band, but found drummer John Densmore and the Morrison estate uncooperative.

The most frustrating propositions are groups led by drummers, the musicians least likely to have contributed to the songwriting or signature sound. Brummie Bev Bevan has been guilty of attempting to reform not only the Electric Light Orchestra but also The Move, his previous band, while Geordie sticksman John Steel is touting his Eric Burdon-less Animals. In the US, Fito de la Parra has been "On the Road Again" with Canned Heat since 1967 despite the demise of singer Bob Hite and guitarists Alan Wilson and Henry Vestine.

Dr Feelgood's line-up features no founder member since the three other originals left vocalist Lee Brilleaux in the early Eighties. When he died in 1994, manager Chris Fenwick recruited Pete Gage, and then Robert Kane, who has now passed the 1,000 gig mark with the Feelgoods.

The Drifters have taken the franchise concept to its ultimate conclusion, with a revolving cast of 60 different singers over 55 years. "The Drifters is a contract that a singer enters into," says Tina Treadwell, daughter of the group's original manager. "It's a bit like Coca-Cola."

Singer and broadcaster Paul Jones tours with The Manfreds, featuring Mike Hugg and Tom McGuinness, stalwarts of Manfred Mann, as well as Jones, the group's original frontman, and Mike D'Abo, his replacement.

Genesis floundered in 1997 when they drafted Ray Wilson to replace Phil Collins, but triumphed last year when the drummer and vocalist returned. They could yet tour with both Collins and original frontman Peter Gabriel.

Fans in search of the ultimate brand can look forward to more dates by the Frankenstein monster that is Queen + Paul Rodgers. The group will unleash their first studio album without Freddie Mercury in September. Live, they perform "We Will Rock You" and, you guessed it, "The Show Must Go On".