50 years on from Abbey Road, on Saturday morning the Abbey Road, North London webcam revealed the immemorial gaggle of Beatle fans treading and re-treading the hallowed crossing, all stiff-legged in the approved manner. Now here in the evening were the Oxford Beatles selling out the Sheldonian, the space choked with a kilometre of snaking leads, banks of guitars and kaleidoscope lights, while there below the Chancellor of the University's rostrum throbbed the tech desk. So, was Mozart turning in his Vienna grave at this hijacking of hallowed ground by the Goths and Huns? I doubt it. More likely he'd have been in the Upper Gallery applauding the four fellow possessors of a genius for melody.

And it was Riaz Ahmad, our McCartney for the night, who led us with 'Yesterday' into a first half crammed with songs. An oddly downbeat choice of starter, I'd thought beforehand, but how wrong I was: Riaz was straight into the trappy F Major opening line with perfect pitch. Owning the required vocal range spanning counter-tenor to baritone, often with a hint of vibrato but never over-egging that pudding, he was jauntily lilting for 'When I'm 64', then tender in the ode 'Martha My Dear' with music hall piano from Greg Hooper, a jack-in-the box all night as he swapped keyboards for lead vocals on the hard-driven, semi-blues of 'Lady Madonna' and conducting his 13-strong orchestra. And what depth of sound they provided, from grainy violins in string quartet-mode for 'Eleanor Rigby' to the wall-of-sound with trumpet and piccolo notable for 'Penny Lane' and horn fanfare in 'Martha', and for the most astonishing number of all, 'I Am the Walrus', that atonal masterpiece of unstable chord progressions from jagged cello and double bass.

If Chris Bayne's John didn't quite have the familiar nasal rasp, he lacked for nothing in volume and personality, grinding out 'Walrus' and later rocking in 'Mean Mr Mustard', then splicing into 'Polythene Pam'. Guitarist Tom Blackburn gave us a mellifluous lead line on 'Something', then jangly, chord-melody acoustic playing complete with arpeggio breaks on 'Here Comes the Sun', his guitar sounding almost like a mandolin. After drummer Dan Harris gave us a dynamic Ringo solo in 'The End', the number was driven on by the three guitarists in turn delivering high-speed rock-and-roll solos, perhaps The Beatles' most powerful guitar statement of all.

They'd been cunningly keeping Riaz back until almost last. Suddenly in the encores he attacked the intro-free, belting intensity of 'Oh! Darling'. How taxing was that on the voice after a 28 song set, but up he came, fresh as a daisy, and the seasoned session musicians all around him thumped out their approval at the final chord. Of course we were seen off by a rousing 'Hey Jude' – what else? – before the building tottered under the detonation of the roaring applause.

'Is the next stop the White Album?' I asked Chris Bayne afterwards. 'I suppose it has to be', he replied. Saturday's full house is counting down the days...