I congratulate the right hon. Member for Ayr (Mr. Younger) on his first speech as Secretary of State for Defence. Although I do not agree with everything he said, I think that he gave a competent performance.

I am opposed to development and deployment of SDI, but on grounds that differ greatly from those so far advanced by my colleagues. I should like to make it clear that I reluctantly support the United States' research programme and participation by British companies in that programme, if possible.

As the debate has shown, there are many concepts of the strategic defence initiative— for example, that it will be available only for silo protection, that it will be available for city protection, and that it will be available for complete protection, which is the 100 per cent. umbrella concept. No one knows what will emerge. The hon. Members for Havant (Mr. Lloyd) and for Beverley (Sir P. Wall) are highly sceptical that there will be anything like a 100 per cent. umbrella.

Hon. Members have quoted various sources. In addition, distinguished former American Secretaries of Defence such as Mr. Harold Brown and Mr. James Schlesinger take that view. I dissent to some extent from the view put by the hon. Member for Beverley because I believe that anything less than a 100 per cent. shield would be an appalling waste of resources. I would not want 10 per cent. or 15 per cent. of the Russian warhead inventory landing on NATO countries. That would be the end of civilisation as we knew it.

The 100 per cent. shield would involve not just the SDI but the Americans in reconstituting defences against the manned bomber and creating, ab initio, defences against submarine-launched cruise missiles. That is the element of the threat about which the Americans are most concerned. The cost of creating a threefold defensive system of that sort will be not hundreds of billions of dollars but thousands of billions of dollars—an obscene amount.

I am unhappy about the Reagan concept of the 100 per cent. shield because it is incompatible with the concept of nuclear deterrence. I believe in that concept. That is not a fashionable view in my party at the moment, but I see no reason to change my mind. If one could create an impermeable shield around the United States there would be considerable implications for Europe's defence.

It has been said that it might be possible to create an effective defence against incoming ballistic missiles for western Europe. I am even more sceptical about that than I am about the possibilities of creating such a defence for north America. It is far more difficult to defend Europe against the manned bomber or cruise missiles than to defend the United States. A manned bomber that wanted to reach cities in Canada, let alone those in the United States, would have to cover 4,000 miles of tundra. Nothing could be easier to find in thousands of miles of tundra where the only other warm presence is a polar bear and where there is nothing else metallic. Of course, the fog of war in western Europe would be totally different from war in North America. The Secretary of State knows that it is impossible to guarantee the defence of these islands against attack by manned bombers. I am glad that he has acknowledged that.

It has been argued that SDI is destabilising. I tended towards that view at one time, but I am no longer so sure. It would certainly be true if one envisaged a scenario in which on one day the United States had no effective defence against ballistic missiles and then a short time afterwards had something very close to an effective defence, but that is not likely to develop. As we have heard today, and as everybody knows, Soviet research has been taking place for years in those areas.

In my judgment, it is almost certain that Soviet capabilities lag behind American capabilities, but their capabilities will develop just as the Americans' have. I find it inconceivable that the Americans will be able to produce an effective system of this sort and the Soviet Union will be left with the cupboard bare. I do not think that the accusation of destabilisation is a very powerful argument to use against the SDI programme.

I am a strong supporter of the ABM treaty. I am glad that my right hon. and hon. Friends have acknowledged that in the past. I believe that it is the best way to preserve the principle of deterrence. If we lose that treaty, which we might, the principle of deterrence falls by the wayside.

Several things have been said today about President Reagan's views on these matters. However, we can all take comfort from the fact that President Reagan will not be around for the final decisions, or for more than a couple of years—at least as President. It is certain that funding in the United States will be doubtful after 1988. So far, only one of the likely presidential candidates in 1988 is committed to the programme—Mr. Bush. As far as I know, none of the others has committed himself to the programme, and certainly the members of the Congress with whom I have discussed the matter are extremely reluctant to contemplate the huge amounts of money that would be involved, not only in continuing the research programme but going forward to full development.

I am glad that my right hon. Friend the Member for Leeds, East (Mr. Healey) has come into the Chamber, because I was about to say something about Krasnoyarsk. I would not want to say anything in his absence and I certainly would not want to give him a seminar on any subject, but the difference between Thule, Fylingdales, and Krasnoyarsk is not necessarily what is contained in the phased array radars but the siting of them. Thule and Fylingdales are on the periphery of the territories they are protecting and Krasnoyarsk is in the middle. That is a considerable strategic difference.