I first encountered this film when it was released on VHS by "fabulous". The transfer at that time was poor--presumably there is only one print remaining--and the DVD reissue is little better.
It's surprising to see this described in other reviews as a movie Goon Show. It's not. Doubtless this misconstruction is caused by the appearance of Peter Sellers as Queen Victoria and Valentyne Dyall (appeared in a few Goon Shows). Whilst the Goons indeed found William McGonagall (and Valentyne Dyall) hilarious, this film actually belongs with Spike Milligan's Q series of the 1970s, and veers more towards the punning and near-the-knuckle racial stereotyping common in Milligan's work of that era rather than the absurd, cartoonish and timeless world of the Goon Shows.
The director, Joe McGrath, was best known as a BBC television director, having directed much of Milligan's output and some of the Not Only... But Also... shows. He had however directed a televised Goon Show performance for Thames in 1968.
The film tells the story of the life of William McGonagall, an unemployed weaver and tragedian, and one of the 'worst' poets who ever lived. He's best known for his poems celebrating the completion of the bridge over the River Tay, and subsequently describing its collapse. In fact, it's perhaps unkind to call McGonagall one of the worst poets; his approach where a line could be as long as necessary to get a rhyme in could be regarded as a precursor to rap by 75 years, if you're feeling generous. Here's an extract from The Railway Bridge of the Silvery Tay:
Beautiful Railway Bridge of the Silvery Tay !
That has caused the Emperor of Brazil to leave
His home far away, incognito in his dress,
And view thee ere he passed along en route to Inverness.
Stirring stuff!
All the action takes place in Wilton's Music Hall, Cable Street, East London, which was to feature in the BBC's much-needed Restoration many years later and is still a going concern. I think this film is unique in being made within such confines.
The film is uneven, on a trajectory from comedy to tragedy. Perhaps this reflects Milligan's well-publicised problems with depression. Is the film funny, however? I'm not sure. Milligan's humour doesn't go down as well as in the TV shows of the era. I think he was always better when you could hear his audience laughing, and he'd be struggling to keep a straight face. However, if you can decipher the dialogue from the rather poor print, there are some clever and funny sections on a par with the Q series, and some of the Tay bridge poetry is very dramatic. A New Orleans jazz funeral taking place in Dundee, with a midget coffin-bearer, is an unforgettable opening image.
I'd recommend that anyone who likes Milligan's TV output should try this film, as you're sure to enjoy at least part of it. If nothing else, it is the coming together of 2 of the Goons in a unique curio of British cinema history.