I agree with the prime minister about both the substance of this decision, and about the timing.
It is a vital matter for our national security.
It requires a long-term approach.
And I hope we can work together on this issue for the good of our country.
On this side of the House, we have always believed that Britain should have an independent nuclear deterrent.
And it is good to see that this is now so firmly part of a national political consensus.
When it comes to our nuclear deterrent, there are some straightforward questions to answer.
Should it be replaced? Do we need a submarine-based system? And does the decision need to be taken now?
Our approach to all these questions has been to answer: "Yes".
On the issue of maintaining our deterrent, and therefore ordering a replacement, we believe the case is very powerful.
Those who argue that the world has changed, so that no deterrent is required, entirely miss the point.
Yes, the world has changed and yes continues to change rapidly.
That is the very case for keeping up our guard.
Just as today's threat is so different from that predicted 20 years ago, so today we can't predict the threat we will face in 20 years' time.
Still less can we predict the threat in 40 to 50 years' time, when the next generation of submarines actually will still be in service.
There are some who argue that, because the major threat is now rogue states, it is not necessary to have a submarine-based alternative.
But isn't it the case that the replacement for Trident will cover the period 2025 to 2055, when the nature of the threat is so completely unpredictable?
It may be rogue states. It may be major powers. We should have a credible deterrent to both.
Does the prime minister agree with me that the key issue of deterrence is credibility, and that the key to a credible system is that it isn't vulnerable to pre-emptive attack?
Isn't it the case that all experts agree that, of the three options of land, air or submarine-based systems, the submarine-based system is the least vulnerable?
On the issue of timing, isn't the key here starting the design and procurement process, so that the new submarines are available when the old ones go out of service?
Wouldn't a further life extension programme be costly and uncertain, and potentially leave a gap?
Let me ask about four specific areas.
First, on the number of submarines, will the prime minister confirm that it wouldn't be right to rule out a fourth submarine?
The French deterrent, for example, does require four submarines.
The prime minister said the decision will be taken when we know more about the detailed design.
Will he confirm that the decision over the fourth submarine does not actually have to be taken possibly until as late as 2020?
Second, some have raised questions of disarmament and of legality.
Does the prime minister agree that replacing Trident with a submarine-based system does not hinder our efforts at all to achieve multilateral nuclear disarmament?
Britain is not part of a nuclear arms race.
This is our only nuclear weapon, it is a minimum deterrent, and we have the right to replace it.
On the issue of legality, can the prime minister confirm that maintaining such a deterrent is entirely compatible with the provisions of the Non-Proliferation Treaty?
Third, there is the issue of cost.
The White Paper gives a commitment that the cost would not come at the expense of the conventional capabilities of our armed forces.
What exactly does that mean in terms of the defence budget he is currently planning?
Fourth and last, there is the issue of warheads.
Previous Conservative governments significantly reduced the number of warheads.
The incoming Labour government reduced them still further.
Now the prime minister is proposing yet another reduction.
Is he content that the new total is sufficient to maintain a credible minimum deterrent?
On this issue, as on others, will he recognise that he doesn't have to make concessions to those in the House who do not support the theory of deterrence and who've never supported Britain's independent nuclear deterrent?
Isn't it the case that the prime minister is able to take the right decisions - because he knows that, if he does, he can count on our full support?