This year our MPs are set to vote on replacing our four aging Trident nuclear submarines.

These would be built in the UK at a cost of £ 41 billion, with the new andTrident missile system bought from the USA. The total cost of submarines and missile systems, together with maintaining both, is put at £ 167 billion by the UK Foreign Affairs Committee.

To decide if this would be money well spent, we need to examine their effectiveness in meeting the threats to the UK in the 21st century. For half a century, big missile submarines have been seen as the most decisive weapon in modern warfare. The UK relies on one in four submarines always being ready at sea and being undetectable.

Now this invisibility is under threat of detection by underwater drones and from attack by cyberwarfare to disable the fire and control systems. In 2007, Estonia was the target of the first state-on-state cyber attack by Russia. Could our submariners stay one step ahead of the hackers, while managing to evade the increasingly effective and numerous underwater drones?

The renewed Trident is not due to be in service until early 2030's, by which time the seas are likely to be swarming with anti-submarine drones from many rival powers. At the same time, increasingly effective cyber-attacks could also render Trident obsolete.

Next we should look at an analysis of the threats facing the UK, as given in the National Security Review of November 2015. Tier one (highest) threats included cyber attack, public health, climate change and terrorism. The nuclear threat, presumed to be from Russia, was relegated to level two. How effective is Trident against any of these threats?

Firstly there is the bizarre logic of having hugely expensive nuclear weapons, in order never to use them. Should we rest Britain's national security on a game of bluff, which, if it fails, will bring about the end of civilisation - by Mutually Assured Destruction or MAD? Secondly nuclear weapons have not deterred terrorists, either in London in 2007 or in Paris last year.

Nuclear weapons will not deal with ISIS - only conventional forces will do so.

My conclusion is that Trident is a 20th century weapons system that is rapidly becoming obsolete in the 21st century. We should spend the estimated £ 162 billion cost on tier one threats to the UK, which include public health, climate change and terrorism.

This would give a much needed boost to our overstretched NHS, would help us combat the increasing threat of climate change and would increase the capacity of our conventional armed forces and the police to guard us against terrorism and other 21st century threats. What do you think of these choices?

John Tomblin

Stanier Road

Preston

Weymouth