Cripin Blunt, the Conservative chair of the Commons foreign affairs committee, spoke after Angus Robertson in the debate and he said he would not be voting for Trident renewal.

Earlier, in an intervention, he said that his current estimate was that Trident renewal would have a lifetime cost of £179bn.

• Blunt said Trident renewal would be “the most egregious act of self-harm to our conventional defence”.

I oppose the renewal of Trident because I care about the security of my country. I’m not prepared to be party to the most egregious act of self-harm to our conventional defence. This is a colossal investment in a weapons system that will become increasingly vulnerable and for whose security we will have to throw good money, after bad – in fact tens of billions of it more than already estimated – to try to keep it safe in the decades to come.

• He said it was a threat to the future of the UK.

Then let us not forget the risks that this particular weapon system presents to the United Kingdom. Basing it in Scotland strengthens the nationalist narrative. Ironically for a system justified on the basis that it protects the UK, it could prove instrumental in the Union’s undoing.

• He said that Tory MPs did not care about the cost of Trident and that this was irrational.

The costs of this project are enormous. I’ve asked a number of colleagues privately at what point do these costs become prohibitive? I can’t get an answer, short of those who say whatever it takes. Surely an answer of infinity is completely irrational. It’s not only damaging to our economic security, with a fixed share of our nation’s wealth being spent on defence, this comes at deeply injurious opportunity cost to our conventional defence. At what point do either of these prices cease to be worth paying?

• He said future technology could render nuclear submarines obsolete.

There is a growing body of evidence that emerging technologies will render the seas increasingly transparent in the foreseeable future. Under development are distributed sensors detecting acoustic, magnetic, neutrino and electro-magnetic signatures, on board unmanned vehicles in communication with each other, using swarming algorithms and autonomous operations associated with artificial intelligence, able to patrol indefinitely and using the extraordinary processing capabilities now available and improving by the month. The geometric improvement in processing power means your smart phone is far superior to that of the latest US fighter aircraft. Furthermore, unmanned aircraft will detect the surface wake of deeply submerged submarines communicating with those underwater receiving active sonar. Marine biologists are already able to track shoals of fish in real time from several hundred miles away.

Ballistic missile submarines depend utterly upon their stealth by utilising the sheer size of the oceans. If we are today able to detect the gravitational waves first created by the big bang, how can we be so confident that a capable adversary would not be able to track our submarines 20 years from now?

• He said Trident could be vulnerable to cyber attack.

What about the security of the Trident system from cyber attack? We will be spending several tens of billions on our nuclear weapon system in order to threaten our adversaries with nuclear attack. There is every incentive for them to invest in offensive cyber capabilities at a fraction of this price in order to neutralise them. The systems are vulnerable through the components that are supplied to BAE systems, through the period of assembly, when the submarines are in refit, or when they are being restocked between patrols. The air-gap with the internet provides only minimal protection, as the Stuxnet attack on the Iranian centrifuges demonstrated.

• He said the government should consider cheaper nuclear alternatives.

We should be considering alternatives, such as deploying these modernised free-fall bombs on the new F35 jets we are buying from the Americans. Such a system would be a significant contribution to NATO’s nuclear posture, tailored to the type of threats NATO could face in the worst conceivable scenarios, at a fraction of the cost.

Jeremy Corbyn opposes Trident renewal in Commons debate – live
http://www.theguardian.com/politics/blog/live/2016/jul/18/trident-debate-renewal-corbyn-may-idealism-as-mps-prepare-for-trident-vote-politics-live?page=with:block-578d0b26e4b0ae77712d9fdf#block-578d0b26e4b0ae77712d9fdf