Six for the price of half a dozen a grocer be so greedy? Aren't they being rather greedy? Can we forgive such greed?

SPRING Bonus! Hard on the heels of February Bonus! And January Savers! Multi-buys! Buy-one-get-one-free! Aren't we all fed up with such super-market gimmicks, especially when they appear to conceal enormous price increases for other products? Getting around my local Sainsbury's has become a nightmare as anxious shoppers jostle for their cut-price Basmati rice. Frequently the items on offer appear to be sold out suspiciously early in the day. It grieves me sorely that in the whole of January, I never managed to buy the frozen haddock (reduced from pounds 2.95 to pounds 1.95).

At the same time I'm shocked to discover how much other items on my list have mysteriously increased since the New Year. When I wrote to Sainsbury's to complain, I was told that the January Savers Promotion had proved to be extremely popular with the "vast majority of customers". Sainsbury's insisted that the reductions should not be linked in any way with those products whose prices had increased. "These increases were due to higher prices being imposed by suppliers."

What unfortunate timing! While you were enjoying your two-for-the-price- of-one Extra Light Sunflower Spread, how many of you noticed that your one-litre bottle of Extra Virgin Olive Oil had jumped from pounds 4.85 to pounds 5.35 and then last month up to a staggering pounds 6.25? When you bought those five jam doughnuts and Sainsbury's kindly awarded you another packet, did you notice that they jumped from 75p to 85p as soon as the offer ceased?

The litany goes on. My husband accuses me of becoming the Hetty Wainthrop of SW6 because of my obsession with investigating the mysteries of Sainsbury's prices. What astonishes me is how few of my friends bother to check their bills or to memorise prices from one shopping trip to the next. Sainsbury's claims to have reduced prices on 200 items in recent weeks. How come my shopping bill for a family of four has remained the same?

Two of my favourite wines have jumped in price. A 75cl bottle of Perrier mineral water has increased from 56p to 72p - a 28 per cent increase. Even a basic sliced white loaf has gone from 39p to 42p. (At the same time a Softgrain sliced loaf was part of the February Bonus campaign, reduced from 48p to 38p. How is the pressure from suppliers pushing some loaves up and others down?) Finnish dishwasher detergent was on offer with a pounds 2.50 discount if you bought two. Since the offer ended the price for one packet has increased from pounds 5.99 to pounds 6.25. Sainsbury's 48 Wholeweat Biscuits went from pounds 1.55 to pounds 1.69 and a tin of chopped tomatoes from 23p to 26p. A pack of six pints of semi-skimmed milk has jumped from pounds 1.33 to pounds 1.45 but has since been reduced to pounds 1.42. Did the consumer force this reduction? Heaven knows what may be happening in the aisles I never reach, from cat food to cake mixes. These are just the prices I have memorised; at least 10 increases - mostly of essentials - out of the 50 or so items I buy regularly.

I would probably put up with these gymnastics if I did not have to be so vigilant at the check-out counter. I am astounded by the number of mistakes made by the scanner, or, I suppose, in reality, the store computer. Special offers not registered; multi-buys not recognised; offers advertised in the store but not entered in the computer's memory. I pay my bill, wade through the receipt and two times out of three, there is a mistake. I march up to Customer Services to complain, dig through the bags to find the item, wait while the member of staff goes to investigate and then, on most occasions, receive a refund for the whole cost of the item, not just the discrepancy. It was when I was refused a full refund on one occasion recently that I wrote my letter seeking clarification of Sainsbury's policy.

The reply ignored this point. Instead the company sent me a pounds 10 voucher.A couple of years ago Sainsbury's was the top of the British supermarket tree: it had more customers than any other chain and, on average, persuaded them to part with more cash than any other store. The nation's favourite grocer is favourite no more. It has been overtaken by Tesco, which now, I read, fills 21 per cent of British shopping baskets. Sainsbury's is fighting back - hence all the special offers.

Now battle is joined between Sainsbury's, Tesco, Safeway and Asda to "differentiate" themselves from each other with "initiatives" and "promotions", such as Tesco's announcement of 4,500 new staff as "customer assistants", to unload trolleys, pack bags, fetch forgotten items, replace damaged goods and answer queries. On the surface, it would appear that the customer will be the chief winner of this battle. Sainsbury's reports that its bonus programmes have been a great success. It shifted a year's supply of chicken tikka in two weeks. (In my experience this meant that it grossly underestimated how much cheap chicken tikka the British nation was prepared to eat.)

By my reckoning - unscientific but convincing to me - the shopper gains little from this kind of gimmickry; and I wouldn't be surprised if, in the long run, it did little to help the stores.

What do I really want in a supermarket? Good quality; variety; reasonable, but just as important, consistent prices across the board; well-stocked shelves; knowledgeable and helpful staff and - vitally - a well-informed computer.

Flashy offers when items are sold out in the first hour do not move me much. Nor do other "differentiations" like creches or loyalty cards.

City analysts say that Sainsbury's has lost market share because it has taken its eye off the ball; it has put margins ahead of basic customer service. They have also dismissed the cut-price battle as a "phoney war". My experience suggests that, for once, the City analysts may be right.