Collapsing walls, sloping shelves and years of little progress dogged the worst of the "Do it Yourselfers" who amazingly still managed to show real pride in their work despite its dubious execution. All this is fine, of course, if the DIYers stay put, but rather more worrying if they decide to sell and a buyer isn't in on the secret.
David McKenna, who runs a building company in Bromley, Kent, has become suspicious of the number of jobs carried out by what he is told are cowboy builders who have done a bunk. "One look at the dodgy tools lying around and it's a reasonable guess that it was, in fact, the owner who messed up the job. Doors are always being hung upside down, and I've seen new openings for windows propped up with bits of wood because nobody thought to put in lintels."
But at least he is called in to put things right. The buyers of a huge, newly converted Victorian house in south-east London will not be so lucky. "The owner works in the theatre but has done all the work himself. It is horrendous. Nothing has been done properly, but the worst of it is that, when the painting is done and the floors sanded, it will fool anyone who doesn't get beneath the surface."
Some of the construction work McKenna sees beggars belief. "At the moment I am spending every day looking at an appalling extension built by the owner. Someone must have told him he needed air bricks for a flat roof, but instead of using a couple each side he has used them all the way round. I counted 30 on one wall. People will spend a fortune on materials and then build a wall that looks like the leaning tower of Pisa."
Jokes about DIY enthusiasts have worn a bit thin for Jane Grant. She has become familiar with pretty well every builder's merchant in the Derby area over the past two years as well as the sight of her husband Rod on his hands and knees cursing at some pipe or wire. They took on the challenge of converting vast old offices into a family home and between them have tackled every job, apart from the damp-proofing. "We must be bonkers. It has taken over our lives because every moment we are not at our jobs we are working on the house. At the beginning the prospect of turning somewhere with loads of space into something special was very exciting, but since then we have had sleepless nights. We've been tired, fed up and ended up arguing. Our three children are used to coming home from school to chaos and we haven't had a holiday for four years."
She lives not a million miles from some of the DIYers featured in the ITV programme but is confident that her husband's workmanship is in a higher league. "Even so, he is self-taught, so he tends to come back from the pub with instructions from an electrician drawn on the back of a cigarette packet. It can take a whole day to get one light to work. I do the rushing around and spend hours in plumber's merchants trying to describe what sort of pipe we need. The hardest lessons are that everything costs far more than you imagine, and you have to finish one job before starting on the next, however tempting it is to start on the fun things. But there have been wonderful moments, such as discovering a lovely marble fireplace under layers of paint."
The area just north of Derby is particularly popular with DIYers, with a terrific demand for unmodernised houses, according to Chris Brown of Boxall Brown & Jones. But he warns buyers that the Grants' experience is all too common. "It is hard to price a job if you are not sure what is involved and so you have to be prepared to spend up to 50 per cent more than you had anticipated," he says.
Fear of injury or worse deters most people from tackling plumbing and electrical jobs, but cosmetic work can be done better than by some in the trade. Many of the time-consuming and costly restoration jobs can be done gradually and to enormous effect - handiwork that genuinely impresses. But this purposeful approach is rather different from the equivalent in the home of the man who is always tinkering with his car. Henry Woods, of the London estate agents Douglas & Gordon, says that, although some owners never stop "improving" their property, after 20 years they haven't managed to change the lead pipes.
In residential areas where property values have risen quickly in a short time, there is a temptation for people to become investor/builders overnight. The advice from agents is that thorough checks should be made on such places before buying. They may appear perfect, with paint sparkling, but that's of little comfort if you get an electric shock every time that you take a shower. South of the river is particularly ripe territory for London's DIY entrepreneurs, says Mr Woods. "I walked into one flat to find a man holding an enormous saw designed for cutting logs. He was trying to cut a thin ply-and-Formica top with it. The whole kitchen was terrible, a complete disaster and held together roughly with nails. The couple were doing it up to sell. Needless to say it didn't."