At the 1994 British Comedy Awards, Spike Milligan famously responded to a tribute from Prince Charles by calling him a "grovelling little bastard". The following day, he compounded the treason by sending the Prince a telegram saying: "I suppose a knighthood is out of the question."

Milligan has always been a one-off, a comedian whose uniqueness stems from just such a disregard for convention. A man who often doesn't give a monkey's for what other people think, he could have a copyright on the word "iconoclast". Notoriously moody, he sometimes refuses to let journalists in for pre-arranged interviews at his gloriously situated hilltop house near Rye. I was lucky enough to be granted entry for a compelling mixture of the riveting, the rib-tickling, the ranting and the rambling. His walk may be shambling, but his talk is still agile.

As he approaches 80, he is held in awe by comedians of every post-war vintage. Frank Muir has described him as "the nearest thing to a comic genius we have had since the war", while Bernard Levin dubs him "a great clown". Milligan's oblique, sometimes impenetrable humour is always original and has spawned any number of surrealistic and absurdist imitators. He has influenced not only his celebrated contemporaries from the 1950s - fellow Goons Peter Sellers, Michael Bentine and Harry Secombe - but also subsequent generations who have gone on to claim greatness in their own right. You can trace the lineage from Beyond the Fringe through Monty Python and Not the Nine o'Clock News to alternative comedy and such modern-day titans as Armando Iannucci, Eddie Izzard and Reeves and Mortimer.

Milligan relaxes in a red velvet armchair, taking in the wonderful view through his living-room picture-window down to the south coast. He says: "I was the founding father of abstract comedy, changing people's minds with an idea they didn't expect. Have you read Finnegan's Wake? I was very interested by that. It was sheer lunacy. The like of the Goon Show will never come again, I don't think. Every time I started to write, I thought I was getting deeper into abstract. That type of humour is getting further away now. I watch American comedies and they are as funny as a baby with cancer... I can't stand punchlines. I've never done, 'I say, I say, I say'. I found loony comedy to my taste."

The good people at the BBC obviously don't, however. Despite repeated requests from Milligan, they have failed to re-show the five runs of his inspired Q series in recent years, much to their creator's chagrin. "It's non-stop pure invention, and the bastards will not repeat it," he says, failing to conceal his bitterness. "I wrote to a BBC executive and said, 'Dick Emery is dead, why don't you give a living writer a break?' He didn't think the show was funny; it was beyond him. He can always watch EastEnders. Dear, dear, dear."

For the past while, Milligan has contented himself with one-off TV specials (Omnibus, An Audience with Spike Milligan) and writing somewhat uneven spoof versions of classic novels such as Rebecca, Lady Chatterley's Lover and Frankenstein. "Is there some perversity in taking a book like Rebecca, which is a literary masterpiece, and shagging it to death?" he wonders. "They don't deserve to be serious. I have just finished Robin Hood, who on his death bed says, 'Bring me my arrow and my bow and wherever this arrow lands, lay me to rest there.' He fires it, and it lands on the roof of a police car."

A septuagenarian who just can't stop working, Milligan also writes enough poetry to fill several slim volumes a week. A selection of the best is released this week on a BBC audio tape. He started penning verse while suffering from one of his many bouts of manic depression. "When I was in a psychiatric hospital, I was very depressed and I started to write poems. In the end, I realised it was - not boasting - good poetry. 'I have a three-legged dog, his name is Rover, but he keeps falling over.' I wrote that this morning - you have a world premiere here. Something pertinent comes to me frequently. I keep a pad by my bed, and if a line comes, I put it down. Like British Rail, you never know when the next one is coming."

Unpredictable - like the man himself. This has not always made Milligan the easiest person to work with. Frank Muir has revealed that he was never able to have Milligan as a guest on Call My Bluff because the producers were scared of such a loose cannon. "They thought he would fool around," Muir recounts. "It's the difference between talent and professionalism, which are antipathetic in a way. The more professional, the less inspirational."

Slightly hurt, Milligan asks of his alleged unpredictability: "Is that something wrong? British Rail are sometimes unpredictable - do you give them up? What could I do that is unreliable? I could only turn up naked."

From his childhood as the lonely son of a British soldier in India, through his traumatic war experiences, to his serial nervous breakdowns and three marriages, Milligan's personal life has been shot through with sadness. But this has merely served to make his comedy that much richer. "I've sometimes thought I'd like a portable ECT machine so I could put myself out during particularly boring conversations," he jokes, blackly. A living example of Tony Hancock's dictum that "funny is not necessarily happy", Milligan is no grinning jester, but a clown with tears never too far from the surface.

He shows no sign of slowing up. He does 50 lengths of his pool each summer's day, and has just packed out a theatre in Windsor with a one-man show. "People think I am dead," he laughs. "Appearing is like having the ghost of Hamlet's father on the battlements. I felt some of them cross themselves when I came on stage. I am a folk hero now."

'Spike's Poems' (pounds 5.99) and 'The Goon Show: Vol 10' (pounds 7.99) are available on BBC audio cassette. A documentary on The Goons is showing in the 'Heroes of Comedy' slot on Wed 7 May at 9pm on Channel 4


1918: Born Terence Alan Milligan in India, where he was brought up. His father was a soldier

1939: Fought in the war until invalided out after being hit by a mortar in Italy - an incident which brought about his first mental breakdown

1949: After the war, joined up with Harry Secombe, whom he had met at the Central Pool of Artists in Italy in 1945, Peter Sellers and Michael Bentine to create The Goon Show, which ran on BBC Radio until 1960. His friend Jimmy Grafton recalls Milligan's thinking behind the series: "He looked at the world and decided it was peopled with idiots. Therefore, he created his own world of idiots in an extreme form." Milligan shares certain traits with Eccles, the character he played. "I'm a very simple person who doesn't like confusion," Milligan says. "That's why I have moved away from London. Maybe this is Eccles in the country!" He wrote 26 half-hour episodes a year for eight years - which precipitated another emotional collapse. "An average author would have been written out," he says now

1952: The first of three marriages; he has six children

1969-80: Five series of the marvellously surreal sketch-show, Q, for BBC2

1994: Receives Lifetime Achievement Award at the British Comedy Awards