BARROW town centre was tonight filled with the sound of an air raid siren as the shipyard tested its nuclear alert alarm.

BAE Systems in Barrow is required by nuclear regulator, the Office for Nuclear Regulation, to periodically test its nuclear siren.

The alarm is played from loudspeakers positioned around the Devonshire Dock Hall - the main facility where submarines are constructed.

Whilst the possibility of an incident occurring with the nuclear reactor of a submarine is very low, there are a number of precautions that need to be in place.

As well as the nuclear alert siren those living within a designated area close to the shipyard, including schools and businesses, are issued with iodine tablets to be taken in the case of a release of radioactive material into the atmosphere.

The tablets work by flooding the thyroid glands with iodine prior to the exposure to radioactive iodine. This prevents the glands from taking up the radioactive iodine and it will be quickly removed from the body.

The yard in Barrow is currently in the middle of its seven-boat Astute-class submarine programme and work has already started on the early construction phase of the Dreadnought boats.

The four Dreadnought submarines will replace the Vanguard-class boats which carry Trident - thermonuclear warheads which act as the country's nuclear deterrent.

HMS Vanguard, Victorious, Vigilant and Vengeance, built between 1986 and 1998,

At least one of the four boats has been on patrol beneath the waves since 1995.

The Vanguard-class submarines were built with a 25-year life expectancy, taking them into the 2020s.

A vote in the House of Commons on 18 July 2016 determined that the UK should proceed with construction of the next generation of submarines in Barrow.

MPs voted in favour of the replacement with 472 votes in favour to 117 against, extending the programme's life until at least the 2060s.

Dreadnought - expected to cost up to £31bn, with a contingency fund of £10bn, are expected to become operational from 2028, with the current fleet phased out by 2032.

Crispin Blunt, Chair of the Foreign Affairs Select Committee, estimated in July 2016 that the programme would cost £179bn in total over its lifetime.