They are one of the jewels in the crown when it comes to Scottish seafood. So prized are razor clams in kitchens around the world that a battle of wits is now being played out between skippers illegally hunting the molluscs using dangerous 'electro-fishing' techniques, and government inspectors intent on policing the trade in Scottish sea food.

A group of fishermen caught illegally electrocuting razor clams earlier this month during a night-time raid are now facing prosecution or fines of up to £10,000.

As enforcement officers from Marine Scotland approached a boat in the Sound of Jura in the early hours of September 10, fishing gear was unceremoniously dumped overboard. It has since been recovered by divers and confiscated.

According to the government, the razor clams were being harvested in an area that had not been licenced for shell fishing. This meant that they could be poisoned by algal toxins and hence be “unfit for human consumption”.

The raid is the latest in a concerted crackdown on the illegal multi-million pound electro-fishing business. Boats drag arrays of electrodes powered by an on-board generator across the seabed to deliver a shock that forces clams out of their burrows.

The clams then have to be collected from the seabed by divers. In recent years three divers have been killed during electro-fishing operations, with one skipper jailed in March this year for failing to properly protect a diver.

Razor clams, also known as spoots, are regarded as a gourmet delicacy, and have a soft, sweet flesh much favoured by chefs. There is a lucrative market for them across Europe and in the Far East.

The vessel intercepted by Marine Scotland officers last week after an “intelligence-led operation” resulted in the seizure of clams worth up to £4,000 in the Far East. Neither the boat, nor its crew have been named.

The fisheries minister, Richard Lochhead, stressed that the government was determined to enforce the law. “It is vital that our reputation is not damaged by produce caught in waters which have not been classified as fit for human consumption,” he told the Sunday Herald.

“Unsuspecting consumers could catch shellfish poisoning from eating the illegal razor clams from unclassified waters. That is why catching those involved in this illegal activity is vitally important.”

He pointed out that electro-fishing was not currently permitted in Scottish waters. “This will be followed by either a heavy fine or prosecution for those involved. They will not escape lightly,” he warned.

“This case should serve as a clear warning to any others that continue to engage in illegal fishing that they should stop or risk being caught and facing serious consequences.”

Ministers introduced a new permitting system for fishermen in 2014, and increased the maximum fines this year. Recorded catches of razor clams have fallen from 915 tonnes worth £3.1 million in 2013 to 423 tonnes worth £1.6 million in 2014.

Since 2008, there have been 32 cases of alleged illegal electro-fishing around the Scottish coast. Of those, 18 have been fined, five have not been punished, four are with the Procurator Fiscal and five are still under consideration by Marine Scotland.

The taking of razor clams against the law was slammed by the fishing industry. “We totally condemn this activity,” said Dr Tom Pickerell, technical director of the industry body, Seafish.

“Illegal, unreported and unregulated fishing is a serious problem that contributes to overfishing, creates unfair competition, impacts on the reputation of the industry and impedes sustainable fisheries.”

Alex Renton, the food campaigner and writer, argued that more needed to be done. “It's extraordinary that Scottish skippers are still electrocuting the seabed in pursuit of shellfish,” he said.

“It is plain stupid and damaging not just to other fish, but to humans too. Research indicates that the majority of Scottish razor clams are caught this way - clearly the policing and the fines are still inadequate.”

Alex Kinninmonth from the Scottish Wildlife Trust welcomed the government’s move. “Alongside the clear risk to human health in this case, the potential for wider negative effects on marine wildlife from electro-fishing must not be overlooked,” he said.

But David Grieve, a shellfish merchant at Loch Leven near Glencoe, argued that electro-fishing for razor clams was “extremely environmentally friendly”. He has been campaigning to make it legal, by requesting a derogation under European law.

He was disappointed, however, that illegal activity was continuing. “With the amount of illegal fishing still going on, I can’t see Lochhead going to Brussels for a derogation,” he said.