Thousands of seabirds are being killed each year after a massive rise in plastics pollution in the North Sea, according to a new report.

Studies on the bodies of 600 fulmars washed up on beaches revealed that 95 per cent had plastic litter in their stomachs – with an average of 40 pieces of plastic per bird.

One fulmar had 1,600 pieces of plastic in its guts, says the Save the North Sea project, which was set up by volunteers and professional organisations in all countries with North Sea coastlines.

Fulmars – gull-like, tube-nosed birds with a massive colony on St Kilda – are affected because they mistake discarded plastic for jellyfish floating on the sea’s surface.

The south-east area of the North Sea – around the Channel exit to German Bight – is the worst-affected and plastics pollution is not only killing birds but also putting off bathers, contributing to beach clean-up costs and causing fouled propellers and blocked water intakes.

Mark Grantham, of the British Trust for Ornithology, said yesterday: "Plastics pollution is a chronic problem in the North Sea. Heaven knows where some of this plastic comes from. They’ve found everything from balloons to shotgun cartridges in the birds’ stomachs. But the commonest is beads of raw plastic before it is formed."

Fulmars, which are small albatrosses, have been breeding on St Kilda for centuries. They spread throughout northern Scotland in the 19th century and to England, Ireland and Wales by 1930. Fulmars lead long lives, with many reaching 40 and some even living to 100.