The premise of this lengthy documentary – an exhibition of Ken Dodd memorabilia opening in his Liverpool hometown – is by far the least interesting thing about it. Generous praise for the way his widow Lady Anne has been working to maintain his unique comedy legacy is one thing, but it’s the evidence of his peculiar genius that we really want to see.

Indeed, there is plenty of fascinating archive footage here, of home videos, of stage performances and of interviews he gave, serious and not. Meanwhile, comics line up to pay tribute, both now and down the ages. At Dodd’s funeral in Liverpool Cathedral, Jimmy Tarbuck called him simply: ‘The greatest stage comedian I’ve seen in my life.’

This film stresses how this was no accident, emphasising how this ridiculous on-stage figure with tickling sticks, Diddy-Men and daft buck-toothed grin was, in fact, a serious student of the theories of comedy, forever heading to the library to learn more. Many contributors stress how intelligent he was, and he seemed as proud of one Shakespearean role as his immense comedy career.

As well as a chaotic attic stuffed full of props, Dodd left more than 1,000 notebooks, many containing meticulous analysis of how each night’s show could have been improved, others offering more philosophical notes.

© Estate of Ken Dodd

Lady Anne (above with Dodd in their early days) reads one page: ‘It seems to me that many jokes, comedy gags and funny lines are concerned with highly charged concepts, dynamic subject matter. The jokes, stories etc. are about certain matters which in themselves are very emotional. There are amongst the myriad of concepts, -isms, meanings, and containers of meanings, objects, subjects, words, phrases, ideas, thought patterns – amongst all of these certain specific of them are charged, energised, dynamic, stimulating, provoking. These are the things that the comic spirit works with. These are laughter areas.’ 

Goodness knows what all that meant, but it clearly points to Dodd being a complex man, obsessive about his craft. But ‘was he happy?’ proves to be a much more tricky question to answer.

The film doesn’t probe too deep into Dodd’s peculiarities, many of which were exposed at his infamous tax trial, especially his obsession with money and reluctance to spend it, with £330,000 in cash found in his Knotty Ash home. Even his own barrister, George Carman, described Dodd in court as 'a fantasist stamped with lifelong eccentricities'.

In a telling moment from the archives, Dodd is questioned about the case and tetchily, and forcefully, shuts down the line of inquiry, despite his interviewer pointing out that he’s happy to joke about the case on stage. 

Instead, the documentary prefers Lee Mack’s assessment: that Dodd – more than any other comedian – was an entertainer for the sheer love of it. And clearly he was never happier than when on stage, which is sure why he was so reluctant to leave it, with his shows legendary for how late into the night they would go.

The glimpses we get of Dodd at work are all a delight, even though he would always – and rightly – consider TV a ‘second-hand’ medium, compared the ‘living, experiencing now’ of a theatre show and its shared magic. 

Dodd’s thoughts on his craft and how he’s in a ‘double act’ with his audience are as insightful you might expect from his extensive studies. You don’t have a career lasting as long as he did without having some wisdom to impart.

© Estate of Ken Dodd

A Legacy Of Happiness is a wholly positive portrayal of this comedy icon and  despite promising to ‘reveal the private man’ behind the public persona, it gives only a restricted glimpse at that more complex, possibly difficult, character. 

But Doddy’s certainly a one-off worth celebrating. While he had his roots in music hall – and even comic traditions dating centuries before that – he made a unique mark that will never be matched.

» Watch Ken Dodd: A Legacy Of Happiness on iPlayer. Also available is Dodd’s in-depth 1996 Face-To-Face interview with Jeremy Isaacs and the 2007 Arena documentary about him.