Radioactive waste from the Sellafield nuclear plant in Cumbria is contaminating shellfish hundreds of kilometres away on the west coast of Scotland, according to a new scientific study.

Scottish researchers discovered traces of radioactive carbon discharged from Sellafield in the shells of mussels, cockles and winkles as far north as Port Appin in Argyll, 160 miles from the notorious nuclear plant.

The findings are a “wake-up call” for anyone who thinks pollution from Sellafield is yesterday’s problem, say campaigners. Sellafield, however, stresses that the contamination is well below safety limits.

The study was carried out by a team of scientists from the Scottish Universities Environmental Research Centre in East Kilbride and The Scottish Association for Marine Science in Oban. It has been published online in the Journal of Environmental Radioactivity.

The scientists found raised levels of radioactive carbon-14 in shellfish sampled at Port Appin, at Maidens in South Ayrshire and at Garlieston and Kippford on the Solway coast of Dumfries and Galloway. Mussels were most contaminated “due to the surface environment they inhabit and their feeding behaviour,” they said.

The contamination comes from Sellafield, which has poured huge amounts of radioactivity into the sea, researchers concluded. The plant, which reprocesses spent fuel from nuclear power plants in Scotland and across the UK, has discharged an average of more than eight million megabecquerels (measure of radioactivity) of carbon-14 a year from its pipelines between 1994 and 2013.

The levels peaked in 2003 but have remained “relatively high”, the scientists pointed out. Carbon-14 persists for tens of thousands of years in the environment and the amounts emitted from Sellafield make up the largest contribution to the long-term collective radiation dose across Europe from the entire nuclear industry.

“This is the first study to have shown that radiocarbon is accumulating in areas remote from Sellafield like Port Appin,” the lead researcher, Kieran Tierney, told the Sunday Herald.

“The enhanced activities we found are due to authorised Sellafield discharges of radiocarbon and they, including the higher activities close to Sellafield, do not pose any radiological risk.”

Dr Ian Fairlie, an independent radiation consultant, described some of the carbon-14 contamination as “surprisingly high”. At Garlieston near Dumfries concentrations in mussels were almost three times the normal background level, while at Port Appin, north of Oban, they were 20 per cent higher.

“As few, if any, shellfish are eaten from the west coast, these increases are probably not dangerous,” he said. “If they were eaten, the increased risks would be low, but it's regrettable that the west coast of Scotland - one of the most beautiful unspoiled parts of the UK - should be polluted by radioactivity in this way.”

Michael Russell, the former SNP minister and MSP for Argyll and Bute, promised to raise the contamination with the Scottish Environment Protection Agency (Sepa). “This demonstrates yet again that there is no such thing as a contained, safe, non polluting nuclear site,” he said.

“The contamination will last for a very long time even if such places are closed at an early date. It is very foolish for the UK Government to continue to encourage nuclear activity which has been rejected by the vast majority of Scottish MPs and MSPs.”

Pete Roche, an energy consultant and editor of ‘no2 nuclear power’ website, said: “This is a wake up call for anyone in Scotland who thinks contamination from Sellafield is yesterday's problem.”

He pointed out that waste fuel from nuclear plants at Torness in East Lothian, Hunterston in North Ayrshire and Dounreay in Caithness will continue to be reprocessed at Sellafield until at least 2018. “Radioactive discharges will continue to flow back in the other direction long after that,” he argued.

Sellafield’s spokesman, Darren Ennis, stressed that the site operated within a stringent and highly monitored environmental regulatory regime. “Marine discharges remain at historic low levels,” he said. “All discharges are well below permitted levels.”

He pointed out that emissions were comprehensively monitored, published and reviewed. The radiation dose from carbon-14 to the most exposed group of people near Sellafield was a tiny proportion of the public health safety limit, he said. “The dose further away from Sellafield will be even lower than this.”

Sepa said that, along with other agencies, it monitored Sellafield discharges around the Scottish coastline. “As concentrations have been identified as low, there is no cause for concern by the public or for the environment,” said the agency’s senior specialist scientist, Mark Toner.