So it's about the money, is it? The Monty Python team, all abundantly equipped with evasive middle-class charm, have pretty much ducked the admission that their reunion next summer at the O2 arena is driven by lucre. Many reasons have been cited, generally in a larky spirit that avoids anything too nakedly mercantile, although John Cleese last weekend, again ostensibly light-heartedly, said that they needed to help pay off Terry Jones's mortgage.

So when, sitting in his agreeable study in one of north London's leafier environs, I get the opportunity to check with the man who played Mr Creosote and Brian's mother whether Cleese was joking, the answer comes as a surprise. "The thing is," Jones explains, "I have an interest-only mortgage and I have to pay £700,000 in 2015, so it's true, yes."

Jones is famously nice (like his friend and long-term writing partner Michael Palin), and nice people make notoriously disappointing interviewees. So this degree of candour, moments into our conversation, is encouraging. But surely Jones has been around the media block too many times to throw out too many hostages. I press on, suggesting that the keenness of individual Pythons to regroup might be in direct proportion to the size of their bank overdrafts. "I don't think any of us have got overdrafts apart from paying off the mortgage," he says. He declares himself "blown away" by the tickets for the reunion selling out in 43.5 seconds.

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The Pythons seems to agree that the most dispiriting words in the English language are "here are a couple of numbers from the new album". The show will consist of tried and tested Python fare, with what Jones calls "some leavening of up-to-dateness" – but precious little, I gather. And to a suggestion that they might do some off-the-cuff stuff, he says with some certainty: "We don't ad lib."

Jones seems to relish the challenge of doing 10 live shows with his Python confrères, and, at 71, his CV still requires frequent updating. The day we met last week, he had had lunch with Elva Corrie, the co-producer, with lyricist Jim Steinman, of Nutcracked, a new musical version of Tchaikovsky's The Nutcracker. ("We're angling it for Broadway," he says confidently.)

He is also preparing for the filming in the spring of Absolutely Anything, which has been 20 years in preparation and is about a teacher at a sink school who has unsuspected magical powers.

And, later this month, the National Theatre of Wales is putting on an adaptation of his Fairy Tales, which include "The Beast with a Thousand Teeth", "The Glass Cupboard", and "The Butterfly Who Sang", and were written more than 30 years ago for the children from his first marriage. The stories are of a piece with the pretext for this interview, which is the paperback publication of Evil Machines, a collection of short stories about devices which behave unpredictably. They include "The Truthful Phone", "The Nice Bomb" (which offers to make a cup of tea) and "The Lift that Took People to Places They Didn't Want to Go".

Much of Python's popularity in the early 1970s was down to the novelty of its absurd, convention-breaking humour. And the stories, published by a crowd-funding outfit called Unbound, are a reminder of Jones's undimmed faith in the power of silliness. He purrs contentedly at his chapter titles, and agrees they belong in the literary tradition of nonsense, as practised by Edward Lear.

In fact, Jones has criticised much of Lear's type of nonsense for not having much of a point to it. But isn't that the point of nonsense – that it has no point, I suggest. He agrees, and also agrees that there isn't really much point to Evil Machines, other than to entertain. He admits, though, that he does get very cross with his scanner.

He also has a record of getting angry, politically at least. "I can't bear politicians," he says. "I don't think democracy works, really. Politicians have to do what people will vote for, and that's not always the best thing to do. I do vote for the Green Party, but I'm considering not voting."

I say that he sounds more despairing than cross. "Yes," he chuckles genially, "… not bothering to be cross. Basically, I agree with Russell Brand about voting." What prescriptions does Jones have? "I think we should run politics on the jury system, with 12 good men and true chosen at random from the population. If you trust a jury to incarcerate people, why shouldn't you trust them with the government?" He agrees that it's hardly likely to happen.

For someone whose personality and work involve so much fun and affability, Jones is not big on obvious optimism. Another project on which he is working is a film about the financial crash of 2008, with animations and puppets, showing how our species fails to learn from its mistakes. Does he have a progressive's belief in humans making things better? No. As a student of Chaucer and much else from the Middle Ages, Jones is well placed to know. "I don't think we've changed. We're just the same as we were then, and BC, and the Romans. I don't think human nature changes. I don't think there's any chance of us getting better."

The optimism in his life seems to come from his second wife, Anna Söderström, 30, from Sweden, and their four-year-old daughter. He affects not to be conscious of their age differences, perhaps wishing to flaunt his indifference to the adverse press coverage that surrounded the end of his first marriage. ("I didn't read it.") "She's more intelligent than I am. She's very level … She can turn her hand to anything." He goes into dreamy raptures about her brilliance as a linguist, co-writer, editor and now businesswoman. She is setting up a pop-up shop in fashionable Shoreditch selling Swedish scarves and hats, based on designs from Gotland, where Jones's mother-in-law has a holiday home.

He is loving being a parent again, and has enough energy to do his share of child-minding and dog-walking. But he admits to a frustration: "I'm not writing anything at the moment, that's the problem. That's my primary purpose in life." For one so prolific, it surely won't be long.