How long Britain could really fight for if war broke out tomorrow2 days ago Share Save Frank Gardner Security correspondent Share SaveBBCRussia's full-scale war on Ukraine will soon enter its fifth year. And in the UK, military chiefs have warned we must prepare for war if we want to avoid it. But if the unthinkable happened, and war with Russia broke out, could the UK fight for more than just a few weeks? That scenario, hypothetically, is just one way we could know that a war with Russia had begun, or was about to. It's about whether UK defence has been under-funded for so long that it has now reached the point where the country is dangerously vulnerable in several areas, notably air defence.