It happened 24 years ago and more than 1,300 miles away from the UK. But, for the sheep farmers of Scotland, the effects from the fallout from Chernobyl have only just ended.

An announcement that the industry is finally free of the radioactive material which forced many of its upland farms to be placed under Food Standards Agency (FSA) restrictions has been hailed as "a blessed relief". Some Scottish farmers have been unable to slaughter, sell or even move their livestock without stringent testing and government pre-approval for the past 24 years.

Many of the owners of the original 9,700 UK farms affected are, even now, reluctant to talk about their fight to survive in the aftermath of the 1986 disaster, because of the possible stigma attached. But one, Robert Morris-Eyton, 48, whose family has owned Beckside Farm on the Furness Peninsula for more than 50 years, told The Independent of the strains caused by restrictions he could not be sure would ever be lifted. "There was considerable uncertainty following the incident because we did not know when or even if we would be able to sell livestock again. It was a worrying time; the whole concept was new to us and it took a lot of adjustment on my farm. Imagine facing the possibility of your livelihood effectively being suspended," he said.

The FSA announced a couple of weeks ago that the last Scottish farm had been declared free of radioactive material. But in north Wales, 330 farms remain restricted, along with eight in Cumbria. Before farmers in restricted areas can sell or move any of their livestock, they must have each animal tested.

David Ellwood, 53, who owns Baskell Farm in western Cumbria, is still under FSA restrictions. "I was told they would only last a week, but 24 years later we are still dealing with it," he said. "It has been going on long enough now and really does seem ridiculous. The other farmers are tired of it, too. But I'm hopeful that because Scotland has had the restrictions lifted we will soon follow.

"It has been a real struggle for us because our daily lives are just that much harder; I can't take my sheep to auction as others can. Instead, I have to ring the FSA two or three days in advance. They take three readings of each sheep I want to take to auction, which seems excessive to me," he said.

Affected farmers are entitled to £1.30 compensation per sheep tested. "That payment was OK to begin with but, as the years went on, its value inevitably diminished. By now, it is worth a lot less," said Mr Morris-Eyton, adding: "There were those who thought that the threshold of radioactivity was set too low, but what could the FSA do? The paramount consideration is the safety of the public."

Concern was raised after heavy rain was thought to have washed the radioactive substance caesium-137 on to upland farms in western Scotland, north-west England and Wales. In the Chernobyl disaster, a series of explosions in a nuclear power plant in what is now the Ukraine sent plumes of radioactive material spewing out over the surrounding area.

Large parts of the Ukraine and nearby Belarus were evacuated and a 19-mile "Zone of Alienation" was set up to keep people away from the worst-affected areas. The city of Chernobyl is said to be the largest ghost town in the world.

The UK government's food watchdog monitored the levels of radioactivity in live sheep and began lifting restrictions where it was was deemed there was a low enough risk to the public, set at 1,000 becquerels per kilogram in sheep meat.

Bob Carruth, a spokesman for the National Farmers Union in Scotland, said: "It seems incredible that 24 years after the Chernobyl accident, a small number Scottish sheep farms remained under restrictions on when they could sell their lambs and were required to undergo annual monitoring for radioactivity.

"Only two years ago, five Scottish farms remained under restriction, while in June 1986, immediately after Chernobyl, restrictions were in place on 2,900 Scottish units. It will be a blessed relief for the last affected farm to have now been given the all-clear this summer, and that all farms affected by the fallout from the Chernobyl disaster have now returned to normal marketing of lambs from their flocks."

The effect of radiation

* Two factors led to the imposition of restrictions on the sale and movement of some flocks of sheep in Britain soon after the Chernobyl accident in 1986, which sent a radioactive plume over much of north-west Europe. First, heavy rain over the uplands of Wales, Scotland, Northern Ireland and northern England led to the radioactive elements in the plume being washed to the ground. Secondly, the poor, peaty soils of these upland areas meant that radioactive caesium-137 in the fallout cloud was taken up by plants rather than being locked safely away in the structure of the soil itself.

* Caesium-137 is considered a health hazard because it can easily enter the food chain and be taken up by the body. Sheep grazing on upland grass especially in the summer months are likely in the worst-affected regions to build up levels of caesium-137 that exceed the limit of 1,000 Becquerels per kilogram of sheep meat set by the European Commission in 1986.

*In North Wales, the worst-affected region, some 2 million sheep on 5,100 holdings were originally put on restrictions, meaning that they had to be tested for radioactivity before being sold for slaughter. The number of farms and sheep under restriction in Wales and Cumbria has since fallen sharply and the restrictions were lifted completely in Northern Ireland in 2000.

* Radioactive caesium has a relatively short half-life of 30 years – the time it takes for activity to halve – and it was always anticipated that restrictions would be necessary for up to 20 or 30 years after the accident. Some of the affected sheep that just exceed the threshold can be brought within the limit by allowing them to graze on lower, unaffected pastures for several months before slaughter.

* Originally sheep had to be killed in order for their radioactivity to be measured but scientists quickly developed a portable radiation monitor that could be used on live animals. Officials use the monitors to assess whether the sheep fall below a "working action level" which is set deliberately lower than the official threshold of 1,000 Becquerels per kilogram to allow for variability in the measurements.