You would not expect the Warwickshire showground of the Royal Agricultural Society of England to be the scene of protests and threatened arrests, still less of offensive T-shirts. But so it was on 15 May at the Pig and Poultry Fair. Mark and Gary Prescott wore T-shirts proclaiming: "Maff banned us and Defra doesn't care", and on their backs: "Maff passed a stupid law in haste and Defra won't pay up." Such anti- government slogans proved unacceptable. The brothers were sternly told to cover them up when a civil servant attending a seminar objected. Just to make sure, a Royal Agricultural Society official pointed them out to a member of the local constabulary, who warned the brothers they could be arrested if the slogans became visible again.

Maff, for the uninitiated, was the Ministry of Agriculture, Fisheries and Food, replaced last year by the Department for Environment, Farming and Rural Affairs (Defra). The latter was supposed to be more enlightened and more green than its predecessor. That is not the experience of the brothers Prescott.

The Prescotts are, or were, pig farmers. They are also among the very few such farmers - probably no more than 50, and nearly all of them small - who still use methods that have existed since the dawn of agriculture. They feed their stock on swill, or human food waste, usually taken free from hotels and restaurants.

On 17 May last year, Maff told these farmers they had a week to switch to alternative feeds. It might as well have given them a week to convert their diesel vehicles to petrol. To turn waste into food that can be given safely to pigs requires expensive machinery - for example, under official regulations, it has to be cooked at 94 C for at least an hour. All this machinery, often bought on loans or overdrafts, would have to be written off. Moreover, conventional pig feed is costly. In effect, the farmers were given a week to close their businesses and lose their livelihoods.

The reason for the ban on feeding swill to pigs was that one producer - recently convicted of feeding uncooked swill to his pigs - was implicated in the outbreak of foot and mouth disease. But there is no reason to think that other farmers were flouting the rules - particularly since ministry officers were supposed to check farms quarterly, with additional spot checks.

Giving swill to pigs is environmentally friendly. Since the ban, food waste has been dumped untreated in landfill sites, to be picked over by gulls and rooks, and then dropped, from beaks or in excrement, elsewhere. If anything, the ban made foot and mouth more likely to break out.

Still, Maff's ruling might just have been acceptable if the swill-feeders had been treated like other farmers affected by foot and mouth, and offered compensation. They have received nothing. Not only has Defra ignored their campaign for compensation, so has the National Farmers' Union and the pig farmers' own body, the National Pig Association. The truth is that swill-feeders were always regarded as a bit below the salt, and the agricultural establishment wants nothing to do with them. Like the food waste, they've been dumped.