The Ministry of Defence has been forced to request US military assistance to track a suspected Russian submarine off the coast of Scotland.

Two US Navy aircraft have been conducting anti-submarine patrols in the north Atlantic this week on the trail of a Russian vessel in the area. A Royal Navy frigate has also been dispatched. It is believed the Russian presence could be linked to the reported departure of one of the Royal Navy’s Vanguard-class nuclear submarines from Faslane naval base at Gare Loch on the River Clyde. Vanguards carry Trident ballistic missiles.

Two American P3 Orion maritime patrol aeroplanes were called in to fill what defence experts described as a “gaping chasm” in Britain’s anti-submarine capability following the scrapping of the RAF’s £4bn fleet of Nimrod surveillance aircraft in 2010.

Angus Robertson, the Scottish National Party’s defence spokesman and MP for Moray, said the US deployment showed that Britain had resorted to going to its allies with a “begging bowl”.

Tensions between Russia and the Western world Show all 8 1 /8 Tensions between Russia and the Western world Tensions between Russia and the Western world Russia Vladimir Putin leaves G20 early after criticism from world leaders over Ukraine. David Cameron warned Vladimir Putin, face to face, that Russia’s whole post-Cold War relationship with the West is at a “fork in the road” over Ukraine Getty Tensions between Russia and the Western world Russia A mysterious Russian object is being tracked by space agencies, giving new life to fears about the increase of space weapons. The satellite, dubbed Object 2014-28E, has grabbed the interest of official and amateur satellite-watchers because it is taking a confusing path and its purpose has not been identified Getty Images Tensions between Russia and the Western world Russia Russian warplanes are risking the security of civilian passengers as they play a dangerous game designed to test Western air defences, according to Nato’s secretary general FRA Tensions between Russia and the Western world Russia Russia has warned Ukraine that a resumption of hostilities against pro-Russian separatists in the east would be catastrophic for Ukraine Reuters Tensions between Russia and the Western world Russia A Swedish minesweeper searches for suspected "foreign underwater activity" near Stockholm. A Russian sub in Swedish waters has slipped away into the sea...leaving recriminations in its wake Reuters Tensions between Russia and the Western world Russia Sberbank, Russia's largest lender, is taking the European Union to court in an attempt to loosen Western sanctions imposed over the Ukraine crisis GETTY IMAGES Tensions between Russia and the Western world Russia Russian government agencies have been accused of editing a Wikipedia article to suggest the Ukrainian military was responsible for shooting down the Malaysia Airlines flight MH17, a Twitter account monitoring state IP addresses has claimed AFP Tensions between Russia and the Western world Russia Australia’s prime minister Tony Abbott has promised he will “shirtfront” Vladimir Putin over the downing of Malaysia Airlines flight MH17, which killed 38 Australian citizens AP

Defence analysts said it raised questions about the UK’s ability adequately to protect its nuclear submarines. Sources said “visits” from Russian subs were “happening quite often” off the north and west coasts of Scotland.

This week’s operation follows a deployment last month by maritime patrol aircraft from Canada, France and the US, first revealed in Aviation Week magazine. On that occasion, it was suggested that a suspected Russian submarine may have been trying to track one of Britain’s four Vanguard-class boats after a fishing trawler spotted an “unknown submarine periscope” close to Faslane.

In this week’s search, the US crews co-ordinated with the anti-submarine frigate HMS Somerset, which has been operating off Scotland for a month. According to an aviation photographer at RAF Lossiemouth, the US aircraft, known as Skinny Dragons and usually based in Hawaii, have been flying up to two missions a day since New Year’s Eve.

Peter Roberts, a senior fellow of the Royal United Services Institute for Defence and Security Studies, said: “HMS Somerset is a capable platform and I have no doubt that her deployment alongside these US Navy aircraft is related to the reported departure of a Royal Navy Vanguard ballistic missile submarine from Faslane, and the countering of any Russian deployment from over the horizon.”

The Ministry of Defence has enlisted the help of the US military to search for a Russian submarine near Scotland (Getty Images)

Jeffrey Lewis, a nuclear policy expert with the Monterey Institute of International Studies, said: “I would put my money on it being a Russian attack submarine with cruise missiles on a patrol taking it past Britain and into the north Atlantic and on the US eastern seaboard. The Russians are trying to threaten Nato and Nato is threatening them right back by showing that we can shadow them, and that if they tried this for real we would be able to kill them.”

However, the US intervention has raised questions about Britain’s ability to protect its nuclear fleet. Mr Roberts said: “Ministry of Defence chiefs have been scratching their heads ever since Nimrod was scrapped in a highly political decision. It has left a gaping chasm in the UK’s capabilities and left us highly dependent on co-operation from our allies.”

Plans to equip the RAF with the BAE Systems Nimrod MRA4 aircraft were cancelled in 2010 as a result of the Strategic Defence and Security Review, at which point the project was £789m over-budget and more than nine years late.

The MRA4 was intended to replace the Hawker Siddeley Nimrod MR2, which had been in service since 1969. Its main job would have been to ensure that no foreign submarines could track Royal Navy vessels coming in and out of Faslane. All of the ageing Nimrods, and their planned replacements, were withdrawn despite a National Audit Office ruling that the loss of the aircraft would have “an adverse effect on the protection of the strategic nuclear deterrent”.