There are few more costly ways of making money than property development. Hundreds of thousands, are needed to be a professional developer just for the raw materials and the building. Then there’s the time and labour, not to mention the market research. If it all goes wrong, you could end up bankrupt or in debt for the rest of your life. Given those horrible fates, wouldn’t you at least watch Property Ladder first?

To say it’s amazing Property Ladder has been running for so long with more or less the same formula is an understatement. Each episode goes like this: rich and talented property developer Sarah Beeny visits various amateurs as they try to make a mint from converting some loft into a space-age “space”. She gives them advice on where they’re going wrong. They do their development. She returns at various stages – with continually varying hairstyles and pregnancy bump – to see how they’re doing. At the end, the developers get a few appraisals then try to sell the property. It’s simple, right?

Yet, despite the fact Ms Beeny has been giving more or less the same advice for umpteen series, there seem to be legions of novices for whom it’s all new. Surely even the laziest of these neophytes will have noticed that the formula, which has been constant throughout Property Ladder‘s long reign in Channel 4′s schedules, also demonstrates that anyone who ignores Beeny’s advice ends up regretting it? It happens every single episode. They come up with some stupid ideas, like placing alabaster gnomes in every room as a motif. She tells them to do something more sensible and that’ll cost them less. They ignore her advice. Their plans go wrong. So they change their minds, do as she said, and everything starts to go right again.

But there are apparently so many people willing to ignore Beeny that for at least the last couple of series, the show has been able to up the stakes by following two developers per episode. Neither of them listen, both end up in trouble.

The appeal of the programme for many isn’t just the insight it gives into the complexities of property development, the skills needed and simple schadenfreude. Instead, it’s the sheer number of different faces Beeny can pull when presented with complete idiots, while still remaining diplomatic.

This latest run has been no different from any other in that respect. In the second episode, Beeny was faced with someone who had bought a listed flat at auction without realising he’d have to pay £75,000 to help repair the rest of the block; who hadn’t read any of the sale documents because there were too many of them; and didn’t know what “listed” meant.

She managed to pull an incredible series of faces at each step of the way, something speaking of a lost career in silent movies or gurning, yet never actually lost her temper with the witless wonder who forced his mother to remortgage her house to help him pay for his idiocy. Even when he let slip that he thought Victorian meant 1950s – ’60s did Beeny let rip with bulging eyes and the mild, “What’s a 100 years, hey?” It takes a great deal of comic skill to realise that the unseen audience doesn’t need you to cue the laughter that much when it’s so obviously going to be coming soon.

A further new twist of recent years has been the “revisited” strand that concludes each series. These are repeats of previous series’ episodes, with an extra 10 minutes of footage tacked on as Beeny returns to the original developers to see what’s happened since the series has been made. Miraculously, most of them seem to have grown stupider since the previous series. Tonight, for instance, Beeny returned to find one group now over a million pounds in debt; another developer had somehow managed to develop two properties and begin looking for a third, all without having sold a single site. You’d have thought she would have realised she’d done something wrong along the way, but her response to the multi-millionaire Beeny’s advice? “I’m afraid I’m going to ignore you.” Beeny’s “at least you’re honest” shows what an unrecognised deadpan comedy genius we have in our midst.

The formula is wearing a little thin, it has to be said. We all need a little variety in our lives and there’s not a huge amount from series to series. Occasionally, we’ll get a treat like the man who bought a house in the middle of nowhere that only had a narrow access road. A quick trip with Beeny to a warehouse that sells car turntables enlivened proceedings no end, particularly when he then decided to put a hot tub in the garden. But most are the same kind of development with entrepreneurs making the same mistakes as always: no planning permission, no idea how to project manage, no concept of how to do any work themselves, but an expectation that builders will teach them how to do it.

Nevertheless, the formula still works, and it’s unclear why it still endures. Sarah Beeny’s skills as a presenter and developer give it a certain something. The different kinds of property provide an architectural frisson, too. Wanting to find out which silly idea the developers are going to want to implement next is a lure.

At a deeper, more sub-conscious level, the clear system of morality, in which the badly behaved (those who ignore Beeny) get punished by fate, while those who do good works (those who take her advice) get rewarded, is an additional possible explanation. But when things do go wrong and people suffer serious financial hardship and relationship disasters, Property Ladder becomes almost painful to watch. It’s fair to conclude that the show really hits its stride when nothing too bad happens to anyone, but the stupid do get punished a little bit, at least.

It is perhaps the constant search for the new developer who actually listens to Beeny that keeps us all watching. Like a rare butterfly to a lepidopterist or an endangered eagle to an ornithologist, the smart party who blooms and prospers by following her advice can get us through an entire series of lead-paint sniffing, swaggering fools who want to make money for doing nothing.

Would we want to watch a series populated entirely by smart developers, though? Probably not. Without her clueless straight-men, how could the comic genius of Beeny be exposed?

For as long as she and her ever-changing entourage of the clueless endure, Property Ladder will probably continue. Some tweaking here and there wouldn’t go amiss and just the occasional rare eagle of a savvy developer would help us through the worst patches. But it remains a formula that’s likely to weather changes for some time to come.