From the moment her first book came out in 1971 Delia Smith has been highly influential - people have followed her cooking instructions blindly. When St Delia demonstrates a recipe requiring fresh coriander, her public clear the supermarket shelves of this delicious herb in hours. Her mention of cranberries sent sales of this fruit rocketing and eggs sold in their million once she'd taught us how to boil and fry them properly. Now, in her recent book, How to Cheat at Cooking, she has given the thumbs up to a different style of cooking, which relies heavily on prepared foods, even frozen roast and mashed potatoes! And what's more she has named the producer and the supermarkets that stock these products.

This book, which ironically bears the same title as her first written in 1971, reads like those sponsored cookbooks of 60 years ago, where every recipe contained a brand name. It has arrived in the bookshops at precisely the moment when the public was beginning to question the authenticity of the food they eat, and seek out real food.

Indeed, it has the potential to undo much that chefs such as Raymond Blanc and Jamie Oliver are striving for in one fell swoop. Is this product placement gone mad, or is Delia simply boarding a passing gravy train which could make her a further £30m?

Perhaps I would have ignored this book had I not received a press release from a junk food manufacturer announcing that the Delia effect was now working its magic again. The press release began with the heading "Embrace your kitchen laziness", and went on to state: "It's official - we're all allowed to be cheats in the kitchen - Delia says so."

It then assured readers that we could all put our feet up and relax and whip up lazy meals in minutes, safe in the knowledge that the original Domestic Goddess approves. The press release was promoting a popular range of sauces, which can, it seems, transform a pot noodle in seconds or spice up a tin of baked beans in a trice. All you have to do is open the packet and pour.

Is this press release the first of many that will arrive on my desk, reassuring me that its now OK to talk about commercially prepared ingredients? I fear it might be.

Another aspect of Delia's book which concerns me greatly is the extra packaging her new approach to food shopping will involve. All those bottles and tins containing prepared ingredients, all that plastic wrapping around the frozen potato mash and all that extra energy that goes into keeping such products frozen - aren't these the very things we are all striving to cut down on to curb global warming?

Yet Delia is positively encouraging us to use pre-packaged, ready-made food, bottle of caramelised red onions, for example, or a jar of ready-chopped ginger or roasted peppers. Once Delia would have prepared these ingredients from scratch, leaving nothing on the chopping board to throw away but a few vegetable trimmings.

And the cost of these suggestions! Compare the price of two raw potatoes with a bag of frozen mash and you will see what I mean.

Hours after receiving the sauce company's release, I happened to meet Oxfordshire's Michelin-starred chef Raymond Blanc at The Fishes, North Hinksey and was able to discuss Delia's book with him. We were both attending a fish-tasting session celebrating the Scottish Skippers Scheme, which enables chefs from The Fishes to have a direct link with fishermen who are working in a responsible manner. In other words, we were in an environment where real food was being taken seriously.

He sees what she has done as being completely unethical.

"Suddenly that great lady who helped us all to connect with our food - look for the free-range egg, the organic - has published a book which undermines all her credibility. What she has done is frightening.

"Just at the point where people were beginning to connect with their food, shop more responsibly, more knowledgeably too, and become aware of the joys of regional and seasonal food, she suddenly gives us a completely opposite message, and that's really sad. Anyone who cares about food will be shocked by this."

Raymond accepts that there are some people who don't like preparing vegetables and that the supermarkets have removed this task from them by offering bags of ready-prepared vegetables. He doesn't like this, particularly as Delia's list also includes ready-grated cheese, which loses all its flavour once packed. He recognises, however, that busy lifestyles may push the home cook in this direction.

But when recipes call for items such as tinned minced lamb, ready-roasted peppers, frozen mashed and roasted potatoes and ready-made fresh Italian three cheese sauce, he finds Delia's new approach to cooking unforgivable.

"Are people really too busy to peel a carrot?" he asks, because for Raymond peeling a carrot, or choosing the correct variety of potatoes for a particular dish, is part of the joy of creating a meal.

In Delia's defence, Raymond admits that despite the many food programmes on the television and cookery books at our disposal, people are cooking less and less, and in some ways she is responding to this. However, he adds that Delia is a big name, a brand even, which we have all come to assume responds to certain values.

"She is betraying those values," he said sadly.

The unfortunate thing about all this, we both agreed, is that just a few words from Delia could have endorsed so much that is being discussed at the moment about eating free-range eggs and rearing animals with kindness. Instead of encouraging us to enjoy preparing food, to shop knowledgably and to apply ethical values to the food we consume, she has opened the floodgates, and no doubt inspired many to embrace short cuts the Delia of yesteryear would have thought unthinkable.