My interview with Spike Milligan didn’t exactly go as planned. I made an effort to arrive at his East Sussex address dead on 2pm, so I wasn’t too early, or too late, trying to learn from the mistakes of previous grail-seekers, whose ignominious fates I’d witnessed in a wedge of press cuttings. I did the London journalist/local taxi driver bit that has become a staple feature of all Spike Milligan profile pieces. She recognised the address and was protective and loyal, even in casual conversation. “Let’s just say, he has his good days, like all of us,” she concluded, and dropped me off in a country lane with a name so silly that most journalists can’t resist giving it an improprietous mention. And I joined the ranks of visitors who note that Milligan’s rather squat and functional home is called The Blind Architect and wonder if the name has any significance. I hid my cigarettes in my bag. “He’ll kill you if he sees them,” a south London playwright warned me. “Try hard not to annoy him.”

There’s a short story Ray Bradbury wrote for Playboy in the 1950s that gives a cheesy poetic expression to the modern chaos theories it predates. A man is sent back to the prehistoric era by a newly invented time machine”. He walks above the evolving plant and animal species on an energy pathway that he is warned never to leave.He steps off it for a moment. On returning to his own time he finds the human race replaced by hideous “were-ants in an unrecognisable dystopia. There is a butterfly crushed on the sole of his shoe.

It’s arguable that any time traveller who went to the north African front circa 1941 and accidentally removed Spike Milligan from the equation would find himself returning to a similarly mutated present. “Peter Sellers and I saw ourselves as comic Bolsheviks,” Milligan said last year to a Sunday newspaper of his groundbreaking 1950s radio programme, The Goon Show. “We wanted to destroy all that had come before and to create something totally new.”

In tomorrow night’s Omnibus documentary, which celebrates the man’s life and work, John Cleese candidly admits that without the Goons and, more significantly, Milligan’s late 1960s/1970s BBC2 TV series, Q, there would have been no Monty Python. Q set new boundaries for “broken” comedy, sidestepping the constraint of punchline by a series of neat escape devices, with Milligan leading a set of obviously bewildered, but tolerant, supporting actors into comic landscapes disturbingly unfamiliar to the viewer, but clearly intricately charted in the dusty map room of his mind. It’s not an overstatement to say that Milligan is the wellspring of all the best modern British comedy, from which flows the Pythons, the “alternative” comedians of the 1980s, and finally the surreal flights of fancy of Reeves and Mortimer today, even though he disowns these most recent offspring as noise and nonsense. I make a living out of writing comedy. Without Milligan I’d still be a horticultural researcher. I owe him a great deal.

The buzzwords, catch phrases and scripts of the post-war alternative comedy that Milligan almost single-handedly sired, all learnt off by heart by successive generations, inform every pub conversation in the land and have achieved the status of modern folk tales. The Newbury bypass protestors kept their spirits up by chanting Monty Python scripts to each other from their treehouses. In the wake of the release of a BBC Enterprises video of the best of Q and the Omnibus documentary which Milligan claims not to remember having participated in, even though he is interviewed at enormous length we all have a chance to assess just how different things might have been without him, and to laugh along at some of the funniest and definitely the most original humour of the post-war era. And, above all, I can get to meet Spike Milligan. Cool!

The third Mrs Milligan, Shelagh, opened the door. “Oh,” she said, a little shocked, peering around the frame. Suddenly I felt unwelcome, like a salesman or a historically disliked relation. “You must be from The Sunday Times. We’ve been trying to contact you all morning. We’d hoped you’d have a mobile phone. Spike’s not well today, you see. He’s still in bed and…” I guessed that “not well” was a well-worn euphemism. Something, predictably, must have thrown Milligan out of orbit that morning, and I just didn’t have it in my heart to press the point. I suppose I’ll never get to be Bob Woodward, and I’ll never interview Spike Milligan after all.

“It doesn’t matter,” I said to Shelagh. “I don’t mind, I half expected this, but,” I continue, when it becomes clear she’s just going to leave me standing on the step, “can I come in and phone a minicab back to town?”

Inside, a younger woman appears on a balcony over the hall, and they’re both looking around as if they’re scared of puncturing the silence. “It’s all right,” she says, coming downstairs, “I’ll run you back in the mini.”

So I’m out the back door in seconds and squeezed into a bucket seat, out of danger, and listening to small talk about the weather we’ve been having lately. “Can you tell him it doesn’t matter,” I say. “I think Spike Milligan has more than earned the right to stay in bed any time he likes, if he wants to.” And I hope it doesn’t sound sarcastic, because it wasn’t meant to be.

Milligan’s manic depression is legendary, and it’s tempting to play the “mad genius” trump card in an effort to explain the fantastic quantum leap of comic imagination that his 1950s Goon Show scripts represent. There simply isn’t a precedent for them, and no glib juggling of exacerbating factors such as his arrival in an alien England from the colonial Indian culture he grew up in, or the black humour that was de rigueur on the war-time front line, or his near death in shelling at Monte Cassino and subsequent medical discharge, will explain them.

The best part of the Q compilation video features Milligan dressed up as a Germanic Rhinemaiden in a light comic opera, where, instead of singing his vocal parts, he simply blows raspberries. It is inexplicably hilarious. In the Omnibus documentary it is Denis Norden, of all people, who comes closest to an explanation of Milligan’s skill, which sidesteps cultural and social factors, and concentrates instead on the simple architecture of comedy. “Spike,” he says, “had a feeling for how long things should go on … before they stopped.”

Back at the station I phone the paper from one of those red call boxes I never see anymore. I’m on my own in a Sussex market town in the middle of the afternoon for no good reason at all, and suddenly everything seems strange. Across the car park there are sheep being lined up in red metal pens for shearing, or sale, or slaughter, or something, bleating and jostling. Apparently there was a piece in the Sunday Express, all infidelity and illegitimate children, that had upset Milligan the day before, and I feel vaguely sordid by association with a publicity mechanism that has driven a depressive old man to his bed.

On the train home I wonder if there’s any way of salvaging the piece, and then give up and get talking to a nice woman who wants to quit her job to become an archeologist. A load of pubescent schoolgirls get on somewhere and I duck down out of the way. Later, as they get off, they wave at me and shout catch phrases from Fist of Fun, the television comedy show I co-wrote.

There’s a notebook full of unanswered questions in my bag and a tape recorder I bought from a second-hand electrical shop specially for the occasion. I wish I had the magic Milligan escape engine. “Stands. Walks towards camera. Says, `What are we going to do now?

What are we going to do now?’ Repeat to fade.”