THE Royal Navy has shrugged off concerns over fishing boat safety caused by jamming Global Positioning System (GPS) signals during one of the largest military exercises of its kind in Europe off Scotland's west coast.

The Ministry of Defence has been urged to carry out an immediate review after fishermen lodged "significant" safety complaints over a major multinational NATO ‘war games’ exercise in the past two weeks.

Fishermen are concerned that vessels are receiving little warning for GPS signals to be jammed which has caused navigation issues and what they describe as a "significant" risk to vessels.

Twelve NATO Allies have been participating in the NATO exercise Dynamic Mariner-21/Joint Warrior 21-2 between September 18 and 30.

The Ministry of Defence has been urged to investigate how the exercise is being carried out after the Western Isles Fishermen’s Association (WIFA) raised concerns that vessels in the Minch which rely on GPS for navigation reported received little less than 30 minutes warning that signals would be jammed leading to "extreme disruption and potential danger".

GPS denial operations are routinely done during the staging of Joint Warrior, but were suspended during a staging of the exercise in October 2011 following complaints from fishermen.

The exercise brings together 20 surface ships, two submarines, seven maritime patrol aircraft as well as personnel from Belgium, Canada, France, Germany, Latvia, Netherlands, Norway, Portugal, Romania, Spain, UK and the US.

It runs through a range of scenarios, including crisis and conflict situations, that could be realistically encountered in operations, such as territory disputes, terrorist activity and piracy.

Participating ships arrived at at the Clyde naval base, Hunterston and Greenock.

Part of Joint Warrior, which takes place twice a year in the spring and autumn involves GPS denial operations off the west coast of Scotland which the Ministry of Defence say are conducted at "limited" periods each day.

They say the relevant authorities, especially maritime and aviation, have been involved in the planning process and "relevant safeguards have been put in place".

The Royal Navy has responded to the concerns saying that GPS jamming is "an important part of naval training to ensure ships and personnel are trained and capable of operating without GPS".

They said that they do not publish specific timings of GPS jamming far in advance as these are subject to change.

But they insist that all military jamming activity in the UK is regulated by the telecommunications regulator OFCOM and Ministry of Defence's Joint Spectrum Authority who were "fully engaged" with the planning process and approved all Joint Warrior related activity.

A Royal Navy spokesman said: “Exercise Joint Warrior is subject to long-term planning and follows standard tried and tested procedures, to ensure that any safety and/or environmental issues are fully mitigated, which includes discussions with partner agencies such as the Maritime Coastguard Agency.

“Ahead of the Exercise, a brief was issued to the maritime community via the Queen’s Harbour Master (QHM) Clyde website, which included details of jamming and other exercise activity, and a Radio Navigation Warning (NAVTEXT) was issued to mariners by the Hydrographic Office, with details of the period and area of effect.

“Every effort is made to reduce the impact of the exercise as far as possible via discussions with relevant UK authorities, including close liaison with the Maritime Coastguard Agency.”

The Navy said the Radio Navigation Warning was also re-transmitted throughout the whole exercise.

Duncan Macinnes, chairman of WIFA previous stated: “It’s totally unacceptable for the fishing industry being issued with a navigation warning that their GPS is being jammed within the next 30 minutes.

“This short notice presents a significant risk to vessels relying on GPS for avoiding underwater obstructions whilst they are towing and could result in vessels becoming entangled in obstructions that could result in injuries to crew or damage to vessels if their gear becomes entangled in obstructions."

Angus MacNeil, the SNP MP for Na h-Eileanan an Iar has been raising the issue with the Ministry of Defence so that "proper procedures" for notification over jamming GPS are issued well in advance in future.

He sought an immediate review of the current system of notification to the fishing industry of naval exercises which require the GPS to be disrupted.

In a letter to the UK’s Secretary of State for Defence, Ben Wallace, Mr MacNeil said: “I would urge you to review the current practice of advance notification to the fishing industry prior to the commencement of exercises when GPS or any other systems need to be disrupted.

“A less than 30 minute warning that GPS will be jammed is extremely disruptive and dangerous to the fishing industry and other marine users.

“It is vital that they are fully aware of times of jamming, at least 48 hours before, to enable the fishing industry to plan future commercial fishing operations safely to avoid seabed obstructions which could result in injury to crew or damage to the vessel if the vessel gets caught in any obstruction.

“I am asking for urgent clarification of future intentions for blocking GPS or any other systems for the duration of this joint exercise.”

Some 30 aircraft were due to take part in the exercise with some of them operating from RAF Lossiemouth and Prestwick Airport..

Mine hunting exercises have been taking place around Campbeltown, Loch Ewe, Gruinard Bay, Loch Broom, Little Loch Broom, Enard Bay and Shiant Bank.

Amphibious operations were takong place at Loch Ewe (on private land), Loch Goil and Kyle of Lochalsh.

The exercise also took Cape Wrath Weapons Range, Garvie Island and the North Minch to the west of Ullapool involving fast small boats.