The UK will build "up to" 12 new attack submarines, the prime minister will announce, as the government unveils its major defence review on Monday. The new conventionally-armed, nuclear-powered submarines will replace the seven-strong Astute class from the late 2030s onwards.

Defence secretary John Healey has said Britain must “prepare for war” but admitted ahead of the publication of the government’s strategic defence review he was struggling to halt a decline in the size of the army.