Defence chiefs are facing an inquiry into the safety of the United Kingdom's nuclear deterrent after British and French submarines, each laden with missiles powerful enough for 1,248 Hiroshima bombings, collided while submerged in the mid-Atlantic.

HMS Vanguard, the lead boat of Britain's fleet of four V-class submarines armed with Trident nuclear missiles, limped back into its home port of Faslane in Scotland on Saturday showing significant damage.

Witnesses said the hull was scarred with dents and scrapes.