A British nuclear submarine test saw a Trident missile "dramatically misfired" before it crashed into the ocean.

An "anomaly occurred" during an exercise on January 30 aboard the HMS Vanguard, The Ministry of Defence (MoD) confirmed.

Officials said they could not reveal any more information as the incident relates to national security, but insisted there remained "absolute confidence" in Britain's at-sea nuclear deterrent.

Sources claim the Trident 2 successfully "left the submarine" but "just went plop" into the ocean next to the submarine and sank.

The Trident 2 missile was propelled into the air by compressed gas in its launch tube, however its "first stage" boosters did not ignite, the Sun reports.

HMS Vanguard carried carried out the drill off the coast of Florida while Defence Secretary Grant Shapps was on-board the vessel.

The missile was expected to travel 3,500 miles and land somewhere between West Africa and Brazil in the Atlantic Ocean.

The incident is the second consecutive failed launch after a missile was unsuccessfully fired from HMS Vengeance during a test in 2016.

An investigation into the failed trial has been ordered to determine the cause, while a search will be carried out to recover the Trident 2 from the ocean.

The missiles are designed to burst into the edge of space and track their position, before re-entering the atmosphere and diving back to earth to hit its target.