The thing that people don't seem to grasp here is that a single Trident missile is capable of carrying 10 warheads and is capable of striking 13,000 km away. This means that with a full compliment of missiles, a Vanguard submarine surfacing in Anchorage Alaska would be capable of striking any location in the US (and I believe possibly even Puerto Rico).
A false launch would essentially be capable of ending the world. It was estimated that a small-scale nuclear war of ~50 'Little Boy' air-bursts would have serious global complications. Being that a single warhead on the Trident can detonate at 500KT (25 times a 'little boy'), a single missile launch is equivalent to 5 megatons, all of which could be ground-burst and force more dust into the atmosphere. At 160 warheads and 80 megatons of destruction, the world is essentially over (as we know it) long before a retaliation has ever been launched.
People's response to this never grabs the situation. It always seems to be that people think a false launch could destroy a city like New York, when in reality a false launch from a ballistic missile submarine could easily end the world.
I realize the risks inherent in a lack of safeguards in the Trident program. However, being from the UK and knowing full well that in the event of a nuclear war, my entire homeland will be a nuclear wasteland (too many primary targets in a small area, I know for a fact I lived in between 3 primaries when I was growing up: major harbor, major RAF base, Army training base). So the UK has little chance to approve a nuclear launch after the attack, unless the authorization can be approved by a UK overseas base, fail-safes are just failures in the face of an attack. Fail-safes are intended to prevent unauthorized launches, however for the UK they're also going to prevent authorized launches.
I'm unsure what troubles me more, a poor ability to safeguard the system or the inability for justice if some psycho warlord decides to destroy my homeland.
The UK isn't in the US's situation where a nuclear launch can mean authorization can be granted by a chief of staff or high ranking general before everyone has been obliterated. The US would take potentially hours for a complete destruction, the UK on the other hand can easily be nuked into non-existence inside of a half-hour. A surprise attack doesn't leave much reaction time for the UK like it does the US.