The Liberal Democrats Shadow Scottish Secretary yesterday called for the Department for Transport to hold an urgent inquiry after a rescue helicopter at one of Britain's busiest coastguard stations was grounded for several hours when crew members refused to fly because of a dispute on working hours.

The Shetland coastguard helicopter was stood down from about midday until 6pm after pilots, provided under charter by Canadian firm CHC, expressed concerns that they were close to reaching the maximum 2000 hours flying time allowed under the EU Working Time Directive.

Under safety guidelines, regulated by the Civil Aviation Authority (CAA), civilian helicopter pilots have to observe this annual limit.

The Maritime and Coastguard Agency (MCA) said the dispute concerned the interpretations over the directive and whether non-flying time should count towards the pilots' working hours limit.

The Shetland Coastguard helicopter was not called on for any rescues before agreement was reached at 6pm following urgent talks involving the MCA, CHC and the CAA, which allowed the crew to continue flying.

In the event that a rescue helicopter was needed in the area, the nearest available rescue helicopter would have been used. This could have come from Norway, RAF Lossiemouth, or from BP's bases in Shetland or the Miller Platform in the North Sea.

After the dispute was resolved, Alistair Carmichael, MP for Orkney and Shetland, said: "It is unacceptable that seafarers and offshore workers were left exposed to danger as a result of the Shetland Coastguard helicopter being removed."

A spokesman for CHC said: "The operation at Sumburgh was suspended for a short period today pending clarification of specific legislative points."