Media playback is unsupported on your device Media caption The BBC's Andy Martin: "A huge military exercise is under way in the Irish sea"

A Russian submarine may have been responsible for almost capsizing a UK fishing trawler in the Irish Sea, a UK fishing organisation has said.

The crew of the County Down-based trawler said the nets were snagged and their boat dragged backwards at speed close to the Isle of Man on Wednesday.

Dick James, of the Northern Ireland Fish Producers Association, said the Russian navy may have been observing Nato marine exercises off Scotland.

The UK's MoD has declined to comment.

A Ministry of Defence spokesperson told the BBC on Wednesday that they did not comment on submarine activity.

'Lucky to escape'

Mr James said fishing boats were sometimes damaged by submarines, but added that if it had been a British submarine, the crew would have been obliged to stop and check on the safety of the fishermen.

"It is possible that it was a Russian submarine," he said.

"You cannot always prevent it, but if an incident like this did happen the [Royal Navy] protocols say that the submarine would immediately surface to check on the health and welfare of the people involved and this one did not.

"Paul Murphy, the skipper, said that he sat for five to 10 minutes catching his breath to see if the submarine would surface," Mr James added.

Media playback is unsupported on your device Media caption Skipper Paul Murphy said the boat nearly capsized during the incident

The skipper said his crew was fishing for prawns at a point known as the Calf of Man, close to the Isle of Man, on Wednesday afternoon when the incident took place.

Mr Murphy said they thought they were going to capsize and were lucky to escape unharmed.

Image copyright David Kneale Image caption The crew said the incident happened near to the Calf of Man, an islet off the Isle of Man coast

He described how the trawler was dragged backwards at six knots (nautical miles per hour), something the vessel is not designed to do.

The skipper said there were three tracker systems on board his boat that record its position in the water. He showed a BBC film crew the unusual movements recorded during the incident.

Image caption The trawler's skipper Paul Murphy shows the BBC an on-board computerised tracking system that shows his boat's unusual movements during the incident

Their boat, called Karen, sustained significant damage that could cost an estimated £10,000 to repair.

The Isle of Man government refused to comment on the incident as it took place outside its territorial waters.

'Heightened military activity'

However, one security analyst supported the theory that the Russian navy may have been responsible.

Tim Ripley, who writes for Jane's Defence magazine, told BBC Radio Ulster: "The Royal Navy seem to be saying its not one of theirs. They also speak on behalf of Nato which are our allies, and they co-ordinate Nato submarines in British territorial waters.

"So if it wasn't British and it wasn't American, look to the east. This is an area of heightened military activity.

"The Russians are famous for liking to watch these things and it is a strong possibility that they have sent one of their submarines to watch this activity," the security analyst added.

Earlier this week, RAF Typhoons were launched to intercept two Russian aircraft near UK air space.