The government's Marine Accident Investigation Branch has begun a formal investigation into the sudden sinking of a fishing boat.

The Peterhead-registered prawn fisher Angela sank more than 100 miles north-east of Aberdeen.

All five crew were rescued by a standby vessel from the Scott platform before being airlifted ashore by an RAF rescue helicopter from Lossiemouth.

One man, Michael Simpson, 45, from Buckie, was detained overnight in Aberdeen Royal Infirmary suffering from mild hypothermia.

His four crewmates had got aboard the Angela's liferaft, but Mr Simpson had been delayed and spent 20 minutes in the water.

The stranded fisherman was eventually picked up by a fast rescue craft launched by the standby vessel and directed to him by the men on the raft.

The Aberdeen Evening Express quoted one of the rescued men, Duncan Taylor of Macduff, as saying that it had been an horrific experience.

He added: "We were paddling like mad in the liferaft trying to get to him, but we had to bail water at the same time. I wouldn't like anybody to go through that."

It is not known what caused the Angela to sink, but the MAIB is likely to seek to interview the crew.

A remotely operated camera might also be sent down to the sea bed to obtain video evidence of damage.

Mr Taylor said when the boat suddenly started taking in water frantic efforts were made to stop it listing.

Catch was shovelled overboard but that could not prevent the sinking.

Mr Taylor said: "The deck pump packed up and the water just kept coming. The skipper had a look at the pump, but there was nothing we could do."