The Charisma from Padstow, Cornwall, was boarded by naval officers and inspectors from the fisheries protection vessel HMS Anglesey on Wednesday night and yesterday morning.
After inspecting her drift net it was sealed and a member of the Anglesey's crew left on board to see it was not tampered with. The fishing boat then headed back for Britain and there will be a further inspection when she docks. According to the Ministry of Agriculture and Fisheries, her master could be fined up to pounds 5,000 if prosecuted and found guilty of breaching European Union rules.
The fact that the British authorities suspect a Cornish boat of cheating is a fillip for the Spanish fishermen who have threatened the small British tuna fleet and cut the drift nets of three vessels.
Spain's director of fishing, Rafael Conde, said he was confident the action by HMS Anglesey would help defuse the situation.
Barrie Ball, owner of the Charisma, whose son, also Barrie, was in charge of the trawler, said: 'I can't think of anything that could possibly be wrong with the boat. There's no way I'd send my son down there with all this trouble unless everything was 100 per cent legal.'
The ministry said the action taken by HMS Anglesey showed that Britain's own monitoring and
regulation of its fishing vessels was working. 'Even if it is established that a British vessel has broken the rules there's absolutely no excuse for intimidation and violence at sea,' said a spokeswoman.
The Spaniards, who use lines, hooks and live bait to catch albacore tuna, resent the French, Irish and British fishermen who began using using the more efficient drift nets a few years ago. They believe their livelihoods are threatened and that the rival fishermen are breaking a European Union regulation which outlaws drift nets longer than 2.5km (1.6 miles).
The Cornishmen say their nets, which hang in the water like enormous curtains, are interspersed with large gaps through which dolphins and porpoises can escape. The line of buoys from which they are suspended may appear to be
6km long but the total length of net is only 2.5km, they say.
The albacore tuna migrate into the Bay of Biscay in late July. The Greenpeace ship Rainbow Warrior is now in the fishing area to register the environmental group's protest against drift netting.
The nets entangle all other larger fish and marine life swimming into them. The French drift net fleet - the largest in the North East Atlantic - is estimated to have drowned more than 12,000 dolphins since it got under way in the late 1980s. Even more sharks have been killed.
The European Commission wants all drift netting phased out over the next few years, but has not got the backing of EU member states. It argues that the drift net fishery is environmentally destructive, liable to expand rapidly and difficult to police.