Why is the show so dark? "I'm surprised you say that, because I think it's stories about small triumphs," he replies. "It's about trying to find who you are. Those stories are in there because if you want to find your independence you have to learn to take the rough with the smooth."
And how. In the segment of the show that gives it its title, Morton describes how, at 17, his family away, girlfriend in tow and desperate to lose his virginity, he climbed up the side of his house after locking himself out. He fell 22 feet and several bones, not to mention his priapic dreams, were broken. "There I was, left for the first time as a responsible young adult on my own and that was my sexual awakening."
Morton makes the dark stuff as funny as the slapstick, in a beautifully paced show that draws the audience in with the funnies before the killer punchlines, so shocking and unexpected at times that audiences gasp rather than laugh.
He had wanted for some time to use his childhood but was unsure how to do it. "It was always there and I eventually wrote it down, but I wasn't convinced I could do it on stage. My girlfriend told me to go for it, but I did wonder if it would come across as maudlin, or self-indulgent."
For someone who met with tragedy at an early age - his father's death from cancer and the accidental death of his teenage sister - Morton is remarkably together now. Is it difficult to talk about these experiences on stage? "I've been there and lived them. To relate them is not difficult. If it was an emotional drain I wouldn't do it. And it has been cathartic; when people laugh, you're not alone because it's laughter of recognition. My stuff is personal, but it wouldn't work on stage unless it had universality."
Surprisingly, his remaining family, - two younger sisters - have yet to see the show, even though it was a hit at last year's Edinburgh Festival. "It crossed my mind to talk to them before writing about the deaths, but I didn't. I don't know that we've ever sat down and discussed those things at all." But does he have a right, in talking about his life, to be talking about theirs? "I own my life and I'm telling it from my perspective." But even so... "Not if you do it with candour and sensitivity, and with humour to take the sting out of it. I don't think my sisters, who are fairly garrulous women, would be upset. I really do have the right to talk about anything I want." His expression becomes deadpan: "I speak as a recovering existentialist" and then cracks up.
Like many an autodidact, Morton relishes such a word. He grew up on a housing estate in Cambuslang on the outskirts of Glasgow, and his dad worked at the local Hoover factory. A bright lad, he left school at 16 and did a series of menial jobs and had a brief early marriage. Then in the space of a few months in 1984, Morton sold his home, left his wife, quit his job and went to college. "It was a weird convergence of events."
His quiet demeanour lends credence to the cliched image of a dour Scot; however, Morton is anything but. He relates how delighted he was with the show's reception at Edinburgh where he performed, not in a club, but at the Traverse theatre. After 10 years on the stand-up circuit, Morton might be expected to move into television quiz shows - "I'd rather eat bees" - or even front his own show, a subject that causes the softly-spoken Morton to become animated. "And be famous for presenting? A chimpanzee with a larynx could do it. How can Vanessa Feltz or Carol Smillie be paid millions more than people who keep the streets clean?"
Despite the success in moving his comedy into other areas he is reluctant to write anything serious. But if he did, would it be as dark as Blood Below the Window? Morton is adamant: "I think the show is quite affirming. It says bad stuff goes on in your life, but take a look back and search among the rubble and you'll find some gems there."
`Blood Below the Window' is at Hemel Hempstead Old Town Hall tonight (01442 242827) and on tour until 28 March (details: 0171-287 5010)