Michael Fallon is Secretary of State for Defence and MP for Sevenoaks.

Governments of all colours for the last 60 years have supported an operationally independent nuclear deterrent. It was Attlee and Bevin who in the 1940s argued for a nuclear deterrent with ‘a Union Jack’ on the top of it.

For the last 46 years, Britain has kept a ballistic missile submarine at sea, providing the ultimate guarantee of security against nuclear attack or nuclear blackmail 24 hours a day, 365 days a year. To maintain those continuous patrols, we must take a decision early in this Parliament to build four Successor ballistic missile submarines to replace the four Vanguard boats which become obsolescent at the end of the 2020s. That’s not politics. It’s reality because it takes over a decade to build and trial a nuclear submarine. So we need to get on with this. To do anything else would be to gamble with our national security.

Cold war certainties have been replaced by an unpredictable new nuclear age defined by weapons proliferation, more nuclear states, and rogue nations wanting nuclear weapons and the technology to develop them. An expansionist Russia is commissioning a new class of eight ballistic missile submarines. North Korea has carried out nuclear tests, ballistic missiles tests, and been displaying its long-range rocket capability.

When there are 17,000 nuclear weapons in the world we can’t wish away threats that may emerge in the 2030s, 2040s, and 2050s, the period in which Successor submarines will be in service.

Some argue that the deterrent would not prevent a 9/11 tragedy or halt ISIS’s terror. We have never argued that terrorism should or can be countered by the nuclear deterrent. We are clear that the nuclear deterrent is the only assured way to deter nuclear threats. But we have to deal with both types of threat, and that is what we are doing. Earlier this month, the Prime Minister announced that we will replace the 10 current Reaper drones with over 20 of the very latest model. We can do this because we are increasing the defence budget and creating a new Joint Security Fund with up to £1.5 billion a year of extra funding by the end of the Parliament.

There is a danger that the long-standing consensus will be broken now that Labour has elected a leader who wants to scrap Trident and is not prepared to use it. But there is another tradition in the Labour Party that proudly supports our independent nuclear deterrent. Lord Robertson, the former NATO Secretary-General, and others champion it. Labour MPs were elected on a manifesto to support it. Trade unionists back the deterrent and the strong industrial benefits it brings.

I want to ensure that Parliament stands full square behind the deterrent. MPs have voted overwhelmingly in support of the renewal of Trident twice, in 2007 and again in January this year. That time round, a majority of 327 MPs supported Trident, including 79 Labour MPs who remain in the House.

Today I am speaking to the Keeping our Future Afloat Campaign – a group that includes trade unionists, local authorities and others who represent naval shipbuilding. I will be appealing to all moderate MPs, to put our national security first and to support building four new ballistic missile submarines.

Spending around £25 billion on four 16,000 tonne submarines is a significant sum and we will ensure value for money. This is a national endeavour with a budget nearly three times that of the London Olympics. When spread across the 30 year life of the new boats, this represents an annual insurance premium of around 0.13 per cent of total Government spending.

This investment will support thousands of jobs in the supply chain from Barrow to Berkshire, from the South of England to the North of Scotland. It will also strengthen our world-class advanced manufacturing skills base by keeping our Royal Navy at the cutting edge and inspiring the future brains of Britain – the next generation of engineers, technicians, software developers and designers.

Our deterrent has never been more vital. We are committed to this programme and now we must press on to deliver not just world-class submarines but the security and prosperity that follow in their wake.