THE UK Government is under pressure to reveal more about an apparent hunt for a foreign submarine off the west coast of Scotland.

It has emerged that Nato planes were called in following a sighting of a periscope late last month, in a location in which Royal Navy submarines normally surface as they head into or out of their base at Faslane.

In the House of Commons, SNP group leader Angus Robertson, who speaks for the SNP on defence issues, raised concern that the UK had apparently been reliant on foreign aircraft, provided by the US, France and Canada.

Since the Government scrapped its Nimrods in the 2010 Strategic Defence and Security Review, the UK has lacked a specialist maritime patrol aircraft.

Mr Robertson told Commons Speaker John Bercow: "In the last day news has emerged of a large-scale maritime security operation taking place off the Scottish coast.

"It is doing so in circumstances where the UK MoD is unable to deploy any maritime patrol aircraft and has had to depend on MTA provided by the US, Canada and France.

"Given how serious a situation this is, have you been advised by the MoD that they intend to make a statement to the House so that we as parliamentarians can be informed of this situation?"

Mr Bercow replied: "I have not been so advised. I have no indication a minister intends to make a statement.

"But you have made your point with force and alacrity and knowing you as I do I rather feel that if you consider you have got a good point, you are not likely to let go of it and it is conceivable even that at appropriate points he might repeat it."

At the height of the operation, five aircraft from four different nations with Royal Navy warships were involved in the search for the mystery vessel, according to a report by the Aviation Week journal.

The MoD has said that it had received assistance from Nato allies but would not say whether they had been searching for a submarine.

The episode has drawn parallels with a similar incident in October, when a suspected Russian submarine was believed to have been seen in waters surrounding an archipelago off Stockholm and Swedish defence officials said they there was no doubt that the country's territorial waters had been violated.

Last month the Royal Navy tracked four Russian warships passing through the English Channel while there has been a recent upsurge in incidents of Russian long-range bombers approaching UK airspace.

Jets from RAF Lossiemouth intercepted a Russian Bear bomber as it approached UK airspace last month, one of several near-incursions during the past few weeks.

The Soviet-era Tupolev Tu-95 aircraft was spotted flying in international airspace and "escorted through the UK flight information region". It was the second flypast by aircraft from Vladimir Putin's air force in three days.

Two Bear bombers were also tracked over the North Sea when Nato radars picked up a series of Russian formations engaged in "significant military manoeuvres", ranging from the Black Sea to the Atlantic Ocean.