Killer seals have started eating dolphins in British waters, raising fears they could soon turn on swimmers.

Wildlife agencies across the UK have reported a recent spate of grey seal attacks on porpoises and dolphins, with some being caught on camera.

Horrifying images show a large seal gripping a common dolphin in its teeth in the Irish Sea off the coast of Dublin in January.

Dave O’Connor, from Wolfhound Adventure Tours and the Irish and Whale Dolphin Group (IWDG) said he was watching out for dolphins when he suddenly saw ‘vigorous splashing’.

‘I noticed then that something darker had grabbed onto it and realised then it was probably a grey seal attack,’ he said.

Meanwhile the first suspected case of a grey seal killing a dolphin was recorded in Wales last month.

Experts from Marine Environmental Monitoring said the 6ft (1.84m) long adult female had suffered ‘corkscrew’ injuries consistent with grey seal bite marks.

The gruesome incidents – which also include two suspected attacks in Devon - have raised concerns for the safety of swimmers, with experts warning seal bites can lead to amputations.

‘Half the people I know who work with seals have got bits of fingers missing,’ Cliff Benson, founder of Sea Trust Wales, told The Telegraph.

‘If you do get bitten the bacteria on their teeth are so bad it usually means amputation rather than just sticking a bandage on.’

Last year, Scottish scientists found two beached porpoises had suffered slow, agonising deaths caused by infections from seal bites.

Those who handle the wounded creatures are also at risk of a serious condition called ‘seal finger’, that can lead to sepsis if left untreated.

There are currently around 120,000 grey seals roaming the British coastline.

Dr Izzy Langley, of the Sea Mammal Research Unit at the University of St Andrews, said there was growing evidence grey seals prey on a wider range of marine mammals than previously thought.

She said they already knew about grey seals killing other seals, including harbour seals.

‘But now there is evidence from both direct observations and also from strandings data, that it also occurs between grey seals and harbour porpoises, and common dolphins,’ she told the BBC.

She explained that the unusual behaviour appears to be limited to certain individuals rather than widespread across the population.

Researchers believe the behaviour may involve ambush attacks from below, with dolphins potentially unaware of the threat.

So far, 20 seal culprits have been identified across the British Isles, based on distinct facial scarring – and experts believe they may be learning from one another.

‘I suspect it will be taught,’ said Mat Westfield, co-ordinator at Marine Environmental Monitoring. ‘I think it will be a slow process, but we will see more and more of it.’

Swimmers in the UK are advised not to actively seek to swim with, touch, or feed seals as they are large, wild predators capable of inflicting serious bites and carrying infections.