Bo Diddley, Jazz Café, London

"I'm owed credit for what I accomplished, for what I did to open the door for a lot of suckers."

"I'm owed credit for what I accomplished, for what I did to open the door for a lot of suckers." And still the suckers come: The Fiery Furnaces, The White Stripes, Two Lone Swordsmen, The Raveonettes, The Strokes. These are just a handful of the contemporary acts who have acknowledged the debt that their musical style and attitude owes to Ellas McDaniel - Bo Diddley to you and me - the Mississippi-born self-styled "originator" of rock'n'roll.

Nearly 50 years ago, Diddley infamously sang: "Just 22 and don't mind dying," on his electrifying first hit, "I'm a Man". Yet here he is, at 75, in London, the home of all those other suckers - the Stones, The Animals, The Yardbirds, The Pretty Things, The Clash, The Who - who charged through the door opened by his guitar-driven "shave-and-a-haircut" beat: a choppy, primal rhythm inspired by Southern blues, R'n'B and boogie that set down a groove that has informed everything from punk, breakbeat and heavy metal to, er, George Michael's "Faith".

And he is here because he has to be: eclipsed by bigger, mainly white rock'n'roll acts, this legend's career has been on the wane since the early Sixties, fouled up in legal wrangles with the Chicago blues label Chess over an estimated $50m in sales and royalties that he claims he has never seen.

So was tonight just about the payola, or did the original square-axed "gunslinger" have something else up his sleeve? As the man himself strode languidly on stage in a blood-red suit and coal-black stetson, wielding that home-made oblong Gretsch guitar, the drummer rolled out the signature beat to "Bo Diddley" and things looked hopeful. His keyboardist and bassist - both female - looked as if they should be in a retirement home but provided adequate backing to his rich vocals.

But as the set segued into the reggae chug of "Crackin' up", the atmosphere palled abruptly. This was partly down to the fact that a visibly frail Diddley was seated - and didn't look as if he was going to move any time soon. Stabs at rap and hokey humour kept the likes of Mark Lamarr and Primal Scream's Bobby Gillespie - both here - amused, but the consolations mid-set were the blues numbers, which provided Diddley with a dignified gravitas and showcased his still-remarkable tremoloed guitar-picking.

The pace picked up again with the galvanising swagger of the classics "Who Do You Love" and "I'm a Man", but the gaps between songs - when Diddley expressed his glee at the audience's youth - became longer, and the playing of his band dipped considerably.

As the evening wore on, you couldn't help feeling that Diddley should have been back on his farm, taking a well-deserved nap in his armchair. The crowd were ecstatic just to see him in the flesh, but that question hovered in the air: all about the money? Well, it was on the money in spirit, at least, but the Bo - in terms of putting on a show that does his dark, dangerous legacy justice - is clearly not doing good.