Terry Pratchett - Sir Terry Pratchett, creator of one of fiction's premier higher education establishments - didn't go to university.

"University would have been an absolute tragedy for me," he confides. "I would have found out about beer far too early."

He is the architect and author of the immensely popular Discworld novels (38 titles to date) and has sold more than 65 million books. Discworld is a complex, surreal and yet intriguingly familiar environment where few things reliably are what they seem. A central setting in the series is that venerable academic institution, Unseen University, whose wizard- infested precincts are to be found - or, occasionally, not to be found - in the twin city of Ankh-Morpork.

"UU", as it is known to its myriad fans, appeared in the first Discworld novel, The Colour of Magic, in 1983.

"Why did I write it? Because I thought fantasy was getting silly," Sir Terry says. "So since it was getting silly, somebody who was silly should start to write fantasy - because I got fed up with the post-Tolkien stuff. You know: 'Ho, landlord! A pint of your finest ale!' No one ever says that who is not on drugs ... And so I said, let's write fantasy as if the people are actually real - even if the situations are not."

Since UU first appeared, it has got through an embarrassing number of arch-chancellors, often in distinctly messy and deeply terminal ways, but now it has gained a level of stability under the firm hand of crossbow-toting Mustrum Ridcully.

"It started off as your basic wizarding thing, but you simply know, as a given, that the head wizard has got to be a man with some punch - they are such a rowdy lot. The reason Ridcully has been there so long, and not been knocked off like they used to be in the early days, is that I like him because he is big and brusque, a kind of James Robertson Justice character, but maxed ... ".

But if Sir Terry never went to university, where does he get these memorable - and utterly believable - academic characters and scenarios?

"I worked for the Central Electricity Generating Board - so I know how committees work, and I know how committees can be manipulated - generally around the time the chocolate biscuits turn up.

"Probably these days", he adds with regret, "there are no more chocolate biscuits - because we are all 'tightening our belts'."

The wrangling that goes on in academic committees certainly forms a strong thread through the novels - and once even appeared in the pages of Times Higher Education ("A collegiate casting-out of devilish devices", 13 May 2005), when UU was threatened with the implementation of a quality assurance process.

Another painfully familiar line of narrative is the rather strained relationship between UU and the upstart Brazeneck College in the city of Pseudopolis. This tension came dramatically to a head in the last few pages of his recent novel, Unseen Academicals (2009).

"I liked writing the end where, of course, Brazeneck - I'm very pleased with Brazeneck - has poached people and is trying to muscle in, but it hasn't quite understood everything that it has picked up and now it has this giant chicken running around the place," he says. The chicken is 70ft tall and lays eggs 9ft high.

This flock-up was probably caused by a lack of experience among the staff of the Higher Energy Magic Building at Brazeneck - and provides the arch-chancellor of UU with an excellent platform to demonstrate the preeminence of his staff.

Sir Terry assumes the voice of Ridcully: "We are going to help a fellow university, of course, as we would obviously do - but we are going to let them get a little further in the cacky before doing so ... ".

So does Sir Terry have any views on the current state of higher education in the non-fantasy world?

"Yes, I think we should cut away at it a bit," he says. "I think that when we lost the secondary moderns, we lost our way in dealing with students - first of all, they were thought of as 'students' - and now we seem to believe that everyone will benefit from a university education. They don't, a lot of them - it's a waste of bloody time.

"I think, if a kid in his teens would like to be a fireman, you don't say to him: 'Ah, but you could be an opera singer.' Well, if he hasn't found that out by then, let him go and be a fireman - for heaven's sake, we know we need firemen. And if this kid is good at going up ladders and stuff, well, he is doing a job he wants to do - and that means he will be a happy person and that is going to add to the gaiety of nations."

Inevitably, the reverse is also true.

"We now have lots of people with university degrees who don't think they are doing the jobs they should be doing - because they have got a degree. They haven't quite realised that, tough shit, this was just a way of fiddling the employment figures: 'Did you think that you were going to come out with a career?'"

Sir Terry is keen to remind us that there are other models.

"One of the happiest guys I've ever known was a brickie. One day, he said he wouldn't be in for two weeks as he was going on holiday. I said: 'Where are you going?' He said: 'Oh, I'm going to Egypt. I like scuba diving among the sunken temples in the Red Sea - I've been doing a lot of mapping and that.' It's great! This is a happy man - he had his choices, and I don't think the kids are offered choices now."

To Pratchett, the "choice" facing teenagers is a binary one.

"You either get into university or you don't - and I don't know how you don't get into university - probably by just hanging on to a stanchion and yelling: 'I don't want to go!' We seem to think that 'one size fits all'."

He appears slightly bemused by some of the effects this thinking has had.

"Near where I live is an area with a lot of coppices - old hazel coppices. And just as there were when I first started going there, there are hurdle makers. The only difference is that the hurdle makers in the old days were elderly men with moleskin trousers and their lunch in a pail; these days they are men who have gone through tertiary education. I have a suspicion that they probably tried teaching - and ran away very fast ... ".

Sir Terry's own education was based largely on his passion for reading. "Somehow I kind of shut school out of my mind - but I read absolutely every damn bloody book I could get my hands on."

He has fond memories of one of his first sources of science fiction books.

"It was an old shed, with just a window that you couldn't really see through, where a nice old lady dispensed tea and conversation - and sold eye-watering pornography ... ".

Her sideline was second-hand science fiction, which is what she supplied to the young Pratchett - possibly her one legitimate customer. Many leading science fiction authors have since confirmed to him that "the science fiction bookshop in any town is next to the porno bookshop, or somewhere where ladies of negotiable affection hang out".

When he was 17, Sir Terry left school for a writing job on the local newspaper.

"I think I probably would always have gravitated towards arranging words in order, but I never took any writing courses or anything like that - because working on a newspaper is itself a writing course. In fact, one of the best things any writer can do is work for a while on a local paper. All human life - and death - is here. It is a great shame that there are fewer and fewer local papers."

He recalls his first editor with affectionate amusement: he was apparently "the last person on God's Earth ever to utter the words 'I like the cut of your jib, young man' without being arrested".

Much of his reading over the past few decades has been non-fiction, a great deal of it very old - long-forgotten tomes with titles such as Anecdotes of the Great Financiers - but he has also found time to read every edition of Punch published between 1860 and 1960, a true labour of love. "It amazes me how many words I know - and occasionally use - which are now totally archaic," he says.

His intensely pragmatic approach to learning is graphically demonstrated by a project he recently undertook. Being newly knighted, he felt that he ought to be suitably equipped.

"At the end of last year I made my own sword. I dug out the iron ore from a field about 10 miles away - I was helped by interested friends. We lugged 80 kilos of iron ore, used clay from the garden and straw to make a kiln, and lit the kiln with wildfire by making it with a bow."

Colin Smythe, his long-term friend and agent, donated some pieces of meteoric iron - "thunderbolt iron has a special place in magic and we put that in the smelt, and I remember when we sawed the iron apart it looked like silver. Everything about it I touched, handled and so forth ... And everything was as it should have been, it seemed to me."

As I wrestle with glorious mental pictures of Sir Terry Pratchett ambling through the fields of Wiltshire, sword at his side, we turn to the vexed question of whether creative writing can truly be taught.

"Throughout my career I've pondered on that," he says. "Sometimes I've thought: 'Huh! Creative writing: how can you teach that?' But now, as I get older, I think I'm less certain. There are some people who find out in their late 70s that they are actually good at it - it is finding out what you can do.

"I think you can help someone with the makings of a writer get better. I don't know if you can get someone who isn't in their bones a writer and turn them into one. I would stand to be corrected because I don't want to be dogmatic on this. Where can these theories be tested?"

The profession of writing itself has an almost timeless quality about it, he says.

"I've always thought that the Bible, for example, was written by people like me: smart enough to get a good job in the warm with no heavy lifting."

Once again, images start to crowd into my mind - this time with Sir Terry inserted into an oil painting of the Council of Nicaea, animatedly editing screeds of text on sheets of vellum.

Before any further mental visions can take hold, I ask Sir Terry what the future holds for UU.

"Well, Unseen University is like a jewel - and so you bring it out only rarely. The whole bunch of hoary old wizards arguing with one another - you can't keep that going. It's the same as not using Death too often as a major character."

Until it is needed then, UU will quietly go about its business - until it is taken out again and polished.

"Unseen University, you see, is more or less self-financing - and Unseen University will never die!"

Referring for the first time during our conversation to his very public battle with Alzheimer's disease, he concludes: "Everything now is hinged on my own personal run-time, but I'm pretty certain I shall finish the book I've now started."

He mentions, almost in passing, that he is also writing his autobiography - "because it is always a good idea to get the lies down in print before your enemies actually print the truth". Somehow, I think that it will be well worth reading.