The discovery of a third dead porpoise with apparent bite marks has further fuelled speculation that sharks or a killer whale could be feeding off the north Norfolk coast.

Norwich shoe shop assistant Christina Evans, 58, was on the beach at Overstrand, near Cromer, where she and her partner Malcolm Reeve have a beach hut when she came across the mutilated porpoise with its head apparently bitten off.

Ms Evans, who lives at Keswick Hall, on the Mulbarton Road near Cringleford, said: 'We often watch seals from our beach hut, but the sight of a porpoise was unusual.'

She said they took a photograph of it at the time, in February, but only realised something sinister might be happening when they read yesterday's EDP and saw the story, 'Is a shark lurking off Norfolk's coast?'.

The story recounted how, on consecutive days in March, two dead porpoises with bite marks were washed up at Winterton and neighbouring Horsey.

Mr Reeve, 58, a technician, said: 'I don't want to think about whether there is a shark out there because I like going swimming.'

Dr Ken Collins, a national shark expert at the University of Southampton, concluded the picture of the Horsey porpoise undoubtedly showed a shark bite.

However, EDP naturalist Percy Trett says the attacks are more likely the work of a killer whale.