Billed as "A Musical For The '80s - The 1180s", Cameron Mackintosh's original 1983 production of Blondel was a lavish affair, marking the first time Tim Rice had created a show away from his Superstar and Evita collaborator Andrew Lloyd Webber, and reopening The Old Vic after a major refurbishment. With a cast led by Paul Nicholas and including a young Maria Friedman in the chorus, it wasn't exactly a smash hit but it did well enough to warrant a transfer to the Aldwych where it limped along for a couple of months.

Essentially a light, undemanding show with eclectic and attractive music courtesy of the late Stephen Oliver, it fancifully retells the story of Blondel, a minstrel who, as legend has it, followed Richard The Lionheart off on the Crusades. Rice and Oliver provide G&S-esque patter songs, soft rock power ballads and some rather beautiful choral sections; as written, it certainly doesn't take itself too seriously. To work though, it needs to have a consistency of tone to make the anachronisms, off-the-wall humour and sketchy (to put it mildly) plot and characterisation all gel together. Think Spamalot but without the demented brilliance of Monty Python.

Unfortunately that consistency is fatally lacking from Sasha Regan's workmanlike but uninspired and almost entirely unfunny production, which struggles to achieve a modern relevance and to balance the silliness with something a little more profound. The beautiful new strings-heavy orchestrations and choral harmonies are exquisite (Simon Holt is the musical director) but sit uncomfortably alongside the punning wit of Rice and Tom William's libretto and Oliver's frequently lovely but only intermittently memorable tunes. Chris Whittaker's derivative choreography and Iain Dennis' autumnal hued lighting add to the overall effect of this being like a poor man's Pippin without the menace... or the heart. Some recent rewrites to nod towards current concerns such as Brexit and human rights are clumsily shoehorned in. It feels like the musical equivalent of Ibsen having a bash at a Ray Cooney farce: all over the place.

Unfortunately the cast don't, or rather can't, help. The ensemble singing is truly magnificent but the simultaneous mugging to the audience quickly becomes wearisome rather than winsome, the female chorus apparently in endless audition for Madame Thenardier. The leads - with the exception of Neil Moors' superbly sung King Richard - feel desperately undercast. Jessie May is likeable as Blondel's love interest but suffers from the fact that an already slight part has been further cut down to allow stage time for another - newly created and sadly superfluous - female supporting role, Blondel's Mother (gamely played by Katie Meller, saddled with a bunch of lame jokes about making bad sandwiches, for no very intelligible reason). James Thackeray has neither the vocal chops nor the charisma for the role of villainous Prince John. He has the best song in the score with the barnstorming "No Rhyme For Richard" where he attempts to get Blondel to switch allegiance, but you'd never know it from the fey, underpowered rendition we get here. Admittedly, reimagining the character as a spiteful amalgam of Peter Pan and the Emcee from Cabaret does neither the performer nor the role any favours. Connor Arnold makes a colourless hero as the eponymous Blondel and, like many of the other principal cast members, struggles with the surprisingly rangy demands of the score. The jokey quartet of camp monks who narrate are good value but somewhat outstay their welcome.

Neither vivacious enough to be feel-good musical comedy nor sinister enough to have any edge, this wrong-headed, tedious production makes no case for Blondel as a lost gem. Rather it reduces it to the kind of show where you end up checking the programme to see how many listed songs there are until the interval, then losing the will to live when you realise you're barely half way through act one yet. A dispiriting evening.

Blondel runs at the Union Theatre until 15 July.