Video | Nuclear submarine 'runs aground' off the coast of Scotland

The British Ministry of Defence moved instantly to play down fears, saying it was "not a nuclear incident" and that it had caused no injuries.

One of the UK's latest submarines, Astute is one of a powerful new fleet of four.

It was commissioned at the end of the summer and described as one of the stealthiest ever built in Britain.

A MoD spokeswoman confirmed the collision off the Isle of Skye, saying: "This is not a nuclear incident.

"There are no injuries to personnel and the submarine is watertight. There is no indication of any environmental impact."

She said the vessel was on the surface conducting a "personnel transfer" when her rudder became grounded.

Those in charge of the boat are waiting for high tide before they can refloat it, but do not expect to do so until around 3.30pm.

The coastguard service said it had sent an emergency tugboat to help and still had a vessel standing by in case it was needed.

The submarine's home port is on the Clyde and it has a crew of around 100.

In June 2007 the mammoth 3.5 billion boat was named and launched by the Duchess of Cornwall.

It weighs 7,800 tonnes, equivalent to nearly 1,000 double-decker buses, and is 328ft long.

Its Spearfish torpedoes and Tomahawk cruise missiles are capable of delivering pin-point strikes from 1,240 miles with conventional weapons.

The submarine's nuclear reactor means it will not need refuelling once in its entire 25-year life.