Britain's ability to defend itself against a major military attack has been called into question after an investigation found Navy warships are so loud they can be heard 100 miles away by Russian submarines.

Rear Admiral Chris Parry, a former director of operational capability for the Ministry of Defence, said the £1 billion a piece Type 45 destroyers are “as noisy as hell” and sound like "a box of spanners" underwater.

It comes amid warnings that years of defence cuts and expensive procurement contracts with a small number of large defence firms, has the left the military with an "existential minimum" amount of equipment.