The sigh of relief from Britain's supermarket industry on Friday afternoon, after only the seven processed beef products already known about out of the 2,500 tested came up positive for horsemeat, was almost audible. The big food retailers had been preparing themselves for truly appalling news, for the discovery that hundreds of items contained the wrong kind of hoofed animal. Even allowing for the many more test results to come, this was very good news.

After days of silence from the retailers (with the exception of Morrisons), it was time for the supermarket bosses to break cover; for Justin King, the chief executive of Sainsbury's, to insist those first adulterated dishes were not the tip of some gruesome iceberg; for Philip Clarke, his opposite number at Tesco, to promise to "open up our supply chain".

They could take further comfort from the fact that attention will now shift to the horsemeat found in the offensively cheap food served in state-funded institutions, such as schools and hospitals.

Indeed, that news may be one of the few positives to come out of this story. Campaigners have long insisted there is something truly criminal about the foul quality of food served up to patients and pupils; the discovery that some of it is actively illegal may help to spur the seemingly endless campaign to get something done about it.

But if supermarket bosses think this really is the beginning of the end of their troubles then they are very much mistaken. They would like us to think of the horsemeat scandal as an isolated incident, caused by a change in European Union law last year that barred the use of cheap "desinewed meat" from ruminants, building costs into production and opening the way to fraud. And it may well have had a part to play in this specific set of events.

But that doesn't change the fact. The horsemeat scandal is not some isolated incident. It is a symptom of a much bigger disease affecting mass food retailing in Britain. (Last year's row over falling payments to dairy farmers was another.) It is about the way British supermarkets have singularly failed to react to the vast changes to the global food market that they assumed was theirs to plunder by right.

They assumed they would always be able to buy what they needed at a price that suited them, from all points of the globe. As a result, they did not care that the bad deals they were giving to British farmers were forcing them out of business and destroying the country's agricultural self-sufficiency. Nor, it should be said, did successive governments, which just let them get on with it. The long-fought-for groceries ombudsman, promised in the 2010 election manifestos, will not be in place until 2014 at the earliest and who knows how much power they will wield.

Meanwhile, there has been a seismic shift in the economics of world food. Expanding middle classes in China, Brazil, Indonesia, India and elsewhere have made producers realise they no longer need to deal with British supermarkets and their thuggish approach to doing a deal. Citrus growers in South Africa are refusing to have anything to do with UK plc. Many New Zealand apple growers would rather sell to China, which will pay as much for ungraded, unpacked fruit as the British will pay for graded and packed. It's the same story across meat, dairy and grains.

The price pressures on the supermarkets, desperate not to lose market share, are huge. Morrisons and Asda have started to get rid of the middle men in their supply chain and go direct to the farm gate to reduce costs, but that will only be a stopgap. They have to start paying British farmers more so they can invest in homegrown agriculture, so, in turn, our self-sufficiency will improve markedly. The supermarkets will have to take smaller profits, a fact of life investors will have to get used to. And yes, consumers will have to accept a further increase in the price of food, perhaps from the current 10% of income to 13% or 14%. Otherwise, we will be left at the mercy of the international producers who have no incentive to trade with us and who can charge what they like. Many food staples could double or triple in price.

And scandals such as that around horsemeat in beef products will no longer seem like isolated incidents. They will simply be a fact of life of our increasingly deformed retail food market.

Jay Rayner's book on the challenges of food security in the 21 century, A Greedy Man in a Hungry World, will be published in May