Gordon, Jamie and Nigella are so last year – Channel 4's Come Dine With Me is the TV food sensation of 2009. Lena Corner meets the fans who are living by its rules

When Rhydian Healy invited four friends round for dinner, at the end of the night they didn't just thank him and leave him to the washing up. They stuck around, and gave him marks out of 10 for his efforts. The pizza was tasty and the pancakes were excellent, but it's a shame, his guests all agreed, that he failed to produce a starter. And how on earth, at a dinner party, could he have forgotten to put out napkins?

Telling your host what you really think of their entertaining skills used to be considered the height of rudeness, but now, thanks to Channel 4's cookery show Come Dine With Me, things have changed. Inspecting your host's crêpes suzette and dissecting their beef Wellington is now as much a part of the evening as cheese and biscuits.

The notion of competitive dining was dreamed up five years ago by Granada television producer Nell Butler. The idea was simple: four strangers host a dinner party in their own homes over the course of one week. The meals get marked by the guests and the host with the highest score pockets a prize of £1000.

Come Dine has all the ingredients of classic daytime television fodder - a little bit of cookery, a nose around the contestants' houses and a not-too-hefty cash prize at the end of it. But last year it did something that daytime programmes rarely do – it moved to peak time. Now it pulls in an average of 2.9 million viewers per episode which means, remarkably, the sight of four ordinary people cooking dinner for each other, is one of the most watched things on Channel 4. On Facebook there are now nearly 30,000 members of the Come Dine fan club and, hilariously, on YouTube there are countless videos of people hosting their own copycat competitive dining sessions at home.

The reason it's so popular is that it shows us what really goes on inside Britain's dining rooms. Jamie, Gordon and Hugh might tell us how we should eat, but this is one of the only shows on TV that tells us how we actually do eat. This isn't aspirational cookery it's ordinary, warts and all stuff complete with forgotten ingredients, drunken guests, screaming smoke alarms, allergic reactions and everything else that can mar the perfect dinner party. It certainly puts a kibosh on the irritating perfection of Nigella's cosy soirees.

"It has got an incredible following," says executive producer David Sayer. "I think people really like the fact we're open to anyone who's got a bit of character and is capable of hosting a good dinner party. It gives a glimpse of an unusual, eccentric side to Britain, a side you don't normally see on TV."

Currently there's a debate raging on Facebook about the show's most entertaining character. Is it the woman who turned up to one meal in her wedding dress, or the man who walked around all day with grated cheese in his trouser pocket – 'to soften it up'? Or is it the guy who served a Caribbean main with a side dish of macaroni cheese, or the lady who couldn't remember if she'd put sugar or salt in her tarte tatin?

And which is the most classic episode? Certainly the Preston show, starring the indomitable Valerie Holliday, is a front runner – "My friends love coming round for dinner because my friends adore me and my food" – but whose efforts to compete with the previous evening's 'Hollywood bling night' are hampered when one of her guests starts throwing up.

But culinary hiccups aside, Come Dine tells us everything we need to know about the modern day dinner party.

We are, it seems, a nation of food lovers, albeit with more enthusiasm than flair. It tells us that firstly we will, given half the chance serve vegetables that are overcooked; secondly, when in doubt we always do potato dauphinoise; thirdly, that desserts are generally a choice between crème brulee or something chocolatey. Finally, we are a nation that can't get a decent meal on the table before 9.30pm.

And of course, it reinforces something we already knew: that the British are big drinkers. In some episodes the eating feels somewhat incidental to the drinking. In one, a guest has to lie down on the sofa with a bucket while the others sit finishing their dinner nearby. In another, there is a woman who thought it was OKto turn up with a three-litre bottle of Lambrini as a gift for the hostess, and yet another who thought a 'jus' simply meant chucking a whole bottle of red in a pan and boiling it for a while.

But as well as all this, there are others who stick to incredibly high standards. "I think it does show that we're better cooks than we're given credit for," says Sayer. "It's a myth that British people can't cook and live on ready meals." One episode filmed in Gloucester, for example, saw a contestant both fish and shoot the ingredients for his dinner party, while overall winner Nick Cooper's pork terrine was three days in the making.

The highest-scoring episode ever was recorded in Liverpool; winner Ian Cook scored 39 out of a possible 40 points, and blew his prize money in a weekend. "It was gone in two days flat on two big bar bills in Marbella," he says. Eight months after the show, 44-year old Cook quit his job as a customer services manager for BT and took up cooking professionally. "Come Dine With Me," he says, "fundamentally changed my life." He is now a chef at a much-lauded restaurant in Liverpool called Studio 2.

Come Dine has also changed the life of London-based designer Jenny Collie. "I loved it right from the very beginning," she says. "I think I've seen every single episode that's ever been on." Collier has founded her own, real-life, copycat version called 'Fun Dine With Me', which hosts competitive dining nights at homes in London. It was at one of these that the unfortunate Rhydian Healy, on failing to produce both starter and napkins, came last.

Collier is at pains to keep as close to the format of the show as possible. The contestants are not allowed to be good friends, she attends every meal as a formal adjudicator and the entire event is carefully photographed and documented on her blog.

But there are mutterings amongst Collier's set and other aficionados that things aren't quite what they used to be with the show. Many worry that the producers are starting to do what reality TV selectors do and go for a certain type of wannabe chef.

"Rather than go for a mix of people who are just into food, they're starting to go for caricatures," she says, "teaming the snobby foodie with the argumentative type, for example." And although many people love Dave Lamb's sarcastic voiceovers, Collier thinks he may be getting a little bit too catty. Still, her love of the show is affirmed when she pulls a notebook from her bag stuffed with recipe ideas, shopping lists, as well as a beautifully etched meal plan of her own. "I spend hours and hours planning my own menus," she says dreamily. She's not the only one. Vicky Thomas from Manchester has also been part of a Come Dine circle since last year; in her group, they compete for a £100 prize. "I desperately wanted to go on the show but I didn't get on. So this is the next best thing," she says. "But, let's be honest, isn't giving a verdict what we all did when we left a dinner party anyway? At least, this way, the criticism is done to their face and not behind their backs."

Come Dine With Me: How it works

Contestants on Come Dine With Me all have to submit menus before the start of filming, which ensures that no-one can change their mind halfway through the week. Each contestant is given £125 to pay for ingredients for a three-course meal, including the wine.

The lowest score ever seen on the show was awarded to Lee Pritchett from Wolverhampton who scored a total of seven out of a possible 40. He was penalised for throwing his crème brulee dessert out of the kitchen window. "I was having a bad day and lost my rag," he explains.

The highest score ever was awarded to Ian Cook from Liverpool. He got 39 and missed out on the perfect 40 because he put the water on the table in plastic bottles. "I was lucky," he says, "I was on a show with three other people who understood and appreciated good food."

There have been vegans, vegetarians, pescatarians, as well as carnivores on the show but, controversially, no vegetarian cook has ever won outright; the non-meat eating Sue Thomas from Swansea and Tanya Jay from Kent have both shared the prize money.

There have been eight weeks of celebrity Come Dine With Me. The highest scorer is singer and broadcaster Mica Paris, who got 36 points for her menu of ackee and saltfish, chicken with rice and peas, and lemon vodka sorbet.

The lowest rated celebrity is night-club owner Peter Stringfellow, who scored just 13 after he served olive-oil ice cream, one of his diners found a hair in their food, and the kitchen sink collapsed in the middle of dinner.

The Come Dine With Me format has been sold to 14 countries around the world. It is strangely popular in Germany, where more than 750 episodes have been aired – so far.

'Come Dine With Me' is on Channel 4 at 5.30pm, Mondays to Fridays. To take part in 'Fun Dine With Me', go to Fundinewithme.blogspot.com