A thousand years ago – oh dear, I went for my 25th birthday – there was Side by Side by Sondheim, a revue made from thirty songs extracted from the then impressive canon of Stephen Sondheim including eight each from Company and Follies, but also less-performed works that still contained good numbers, and great musicals for which he’d only contributed lyrics like Gypsy and West Side Story.

But Mr Sondheim, prolific as ever, wrote show after show and producers turned away from Side by Side because it had nothing from Sweeney Todd, Sunday in the Park with George or Into the Woods – and for a long time, Mr S wouldn’t license his numbers to be sung out of the context of the musical for which they were written except for ‘Send in the Clowns’ which he refers to as his ‘only hit’.

Eventually, he relented – by then it can’t have had anything to do with the money and everything to do with the art – and Sondheim on Sondheim scripted by his long-time collaborator James Lapine delivered the same kind of chummy and uncritical narrative alongside material from the later works. When I saw it on Broadway it also provided the still-tuneful-at-80 Barbara Cook with a six foot monitor bolted to the front of the mezzanine from which she could read her words scrolling in 144pt type.

It felt fresher because it included taped interviews with Sondheim at various stages of his career – usually slouching in his studio beside a full ashtray – but also clips from unseen student and off-off-Broadway productions broadcast on about sixty screens which slid up, down and over the stage while the cast sang live.  The design was by Beowulf Borritt, the geeky young man who advertised Windows 10.

The projection has been reduced to a single home movie screen above the stage and so, like Windows 10, this compilation show now feels superseded.

We are well-blessed with astounding musical theatre performers, and there is no doubt that home-grown Damian Humbley and Julian Ovenden, and imported Liz Callaway are among the finest actor-interpreters of this material – Ovenden has a seductive voice and an extraordinary range from baritone to high tenor.  Distractingly, he performs everything while slowly shaking his head from side to side like a horse with earache, but this is a project mainly for radio 3 so perhaps it doesn’t matter.

Humbley was a late entrant to the cast but it gave him a prime opportunity to reprise the angry and musically precise ‘Franklin Shepherd Inc’ from Merrily We Roll Along which made his performance so memorable. Callaway deservedly gets the ripest plums: perfect in ‘Send in the Clowns’ and equally interesting in an unusual mash-up duet with Claire Moore of ‘Losing My Mind’ from Follies and ‘Not A Day Goes By’ from Merrily.

‘Not A Day Goes By’ was the first sheet music I had to learn when I joined the LGMC in 2000 and which we sang in this same location.  Its musical complexities easily defeated my Grade 1 piano sight reading and all but put me off, so it’s a thrill to hear it done so well.

The quartets and sextets are freshened with new arrangements, some illuminating some a touch frantic but they do show how well Sondheim writes for multiple characters each with something to say.  The BBC Concert Orchestra rose to the challenge magnificently, but the shocking sound balance meant the band often overwhelmed the singers.

Two nuggets stood out from the filmed narrative – a casual revelation that his mother told him she wished she had never given birth to him masked what must be real pain, and he explained that he only feels able to write a song when the context and characters are already established by his collaborators.

That was a real insight.