A stranded killer whale highlights the polluted state of our oceans, a wildlife trust said today.

The carcass of the young male orca was found by a bird watcher on salt marsh at Holbeach, near the Norfolk - Lincolnshire border, before Christmas.

Experts from the London Zoological Society (LZS) yesterday took samples from the decomposing creature in a bid to learn more about it and ascertain how it might have died.

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Matthew Capper, head of communications at the Lincolnshire Wildlife Trust, said: "They're incredibly unusual in English waters but there's a pod which commutes between the Western Isles and Shetland.

"It may well have washed up from quite a distance, so who knows where it died." Orcas are apex predators, which are vulnerable to toxins accumulating from prey they consume. Samples taken from the animal by the LZS are now being analysed.

"What they did find was plastic in its stomach," said Mr Capper. "They have said it was not the cause of death but it's another alarm bell over the state of our oceans."

Naturalist Carl Chapman, cetacean recorder for Norfolk, said it was impossible to predict where the animal had come from.

He said: "It will have been dead for quite a while so it could have come from anywhere - a lot further north, a lot further east in the North Sea."

Seals, which orcas prey on, are numerous on both the Lincolnshire and Norfolk sides of The Wash. But the stomach of the whale found at Holbeach was empty.