Rosie Millard: Thrifty Living

Inspired by the example of various fellow thrift-seekers, who have sworn to me the financial worthiness of doing the weekly food shop only at local outlets (interspersed with a monthly haul at Lidl), I decide to spend the last week of the children's holidays without stepping into a single supermarket. This looks quite simple. We are on a self-catering holiday in Cornwall and the sun is shining, so its egg sandwiches and pasties on the beach for lunch. Furthermore, it's the perfect county to choose, since Cornwall's 5,000 campsites have turned it into the national home of the tiny jar of Nescafé, sourced via Londis, branches of which seem to be down almost every village street.

But because people like to take the city with them when they go away, there is also a giant Morrisons up the road. We drive past it snootily. "Ha! We are definitely not going in there," I say, pointing at a whimsical sign directly opposite; "Look, children! True Cornish Fayre. Local Cornish Farm Shoppe. That's where we'll go."

Two days into the holiday and I discover that limiting every purchase to Londis or True Cornish Fayre has drawbacks. First, you have to be very creative with your cooking. True, you will buy hardly any pre-processed meals (good), but you must also face up to preparing supper out of whatever's left at the bottom of the vegetable rack at Londis (not so good). One of our meals has to be prepared from a bag of Knorr savoury rice, and a marrow.

Second, working outside the supermarket model means you have to actually get used to interacting with human beings. This is fine if you are talking to bonny Cornish maids eager to weigh your shallots for you (Cornish Fayre). It's not so great when you are handling bonny Cornish maids fed up with your errant children (Londis).

"Could you please control your son!" the Londis lady shouted at me after the youngest Millard had run riot amongst the Pot Noodles and tanked into a Cornish Pasty-baking oven. I don't blame her, but it's hard. Shopping sans trolley, baby seat, snacks and those handy CBeebies magazines, all within easy reach at supermarkets, means you have to fall back on parenting skills (yes, those) while juggling with a wire basket, five cans of tuna, and a marrow.

Yet does it save you money? Yes, and no. Yes, if you stick to simple, seasonal food, don't mind the odd Heinz label creeping in, and are prepared to work quite hard at the end result.

No, if you decide that pure Cornish Crème Fraiche, locally-churned fudge, packets of tea for £10.99 and wild boar sausages are the only reasonable alternative to a £250 moment at the Morrisons till. The sad truth is that swapping a Morrisons trolley for a wicker basket at Cornish Fayre, or equivalent, is like trading trenches at the Somme.

No matter how free-range the latter is. Simply changing your loyalty from a giant high street name to a posh deli is definitely no help to your debts. You have to forget about being a foodie, in other words, and remember why you are doing this in the first place. You have not shunned spending time in Tuscany and Tesco this summer on health grounds. You have done it on budgetary grounds. You must, therefore, make your decision to sit on a gloriously windy Cornish beach and shop locally work, both as a good idea for a family holiday, and the only choice for a dedicated thrift seeker.

Even if a supper of marrow risotto has made you desperate the next day to book a babysitter and head off to Jamie Oliver's Cornish restaurant where supper comes in at £60 a head, you must not cave in. Eating cheaply one night does not let you off the hook for the next. It just means that you are better prepared to eat just as cheaply the night after. And the night after that.

And when you arrive home sporting that subtle windswept tan only a British seaside holiday can bestow, you can take yourself on a virtuous, virtual journey. You canvisit your online bank account; do that now familiar monthly budget check on your credit cards and find that thanks to your new-found enthusiasm for British beaches and Pot Noodle, they have not been sent spiralling off course. Far from having a September hangover, you will still be on your route to have all your debts repaid by Christmas.