HC Deb 05 September 1939 vol 351 cc438-41
Mr. Aneurin Bevan

(by Private Notice) asked the Minister of Home Security whether he is satisfied that the distinction between the "All Clear" and the warning signals in the case of air raids is sufficiently marked?

The Minister of Home Security (Sir John Anderson)

Yes, Sir. I think the distinction is sufficiently well marked, particularly if people bear in mind that the first signal is always the warning signal and that the signals which follow should invariably be the "All Clear".

Mr. Bevan

Is the right hon. Gentleman aware that there are many Members of this House who had experience of air raid warnings in Spain, and that there it was found that the use of two different kinds of note was infinitely better than merely different lengths of blast on the same note, and that in the case of the "All Clear" tall buildings and drift cause a die-away which makes the" All Clear "warning sound like the original warning?

Sir J. Anderson

Yes, Sir. That matter was very carefully considered, and prolonged research and experiments were made before the existing apparatus for giving the signals was approved. As regards the use of different notes, it is, I think, the fact that many people find difficulty in memorising a particular tone, but no one whose hearing is clear can fail to distinguish between a note sustained for two minutes and a shorter note. There was, I confess at once, in the early hours of yesterday morning a good deal of confusion. That arose from circumstances which have been fully investigated and which should not recur. In fact, a telephonic communication at one point in London was mistaken for a warning signal. A siren was sounded and persons controlling signals round about were left in doubt as to whether they might themselves have made a mistake. The result was that over a considerable period warning signals were given. When the mistake was discovered a well-meant but unfortunate attempt to correct the mischief simply exaggerated the confusion. [Laughter.]I am being perfectly frank with the House. I realise the great importance of making these matters absolutely clear. I think that faulty synchronisation has a great deal to do with the confusion because imperfectly synchronised signals, although each individually is a sustained note, may give an impression of a fluctuating note. I am doing everything possible to secure better synchronisation.

Mr. Arthur Greenwood

While realising that the human factor may sometimes break down, will the right hon. Gentleman go into this question with technicians to get the maximum difference between the warning note and the "All Clear" note?

Sir J. Anderson

That is exactly what I have been doing. There are various possibilities in the direction of intensifying the difference, and these will certainly be fully explored in the light of experience.

Mr. Bevan

While thanking the right hon. Gentleman for his full reply, before he closes his mind to this matter, will he call for reports from the air-raid wardens all over London, because my impression is a very general impression, and perhaps their information might influence him?

Sir J. Anderson

The impression is the one I formed myself.

Captain Peter MacDonald

Would it not be possible to co-operate with the B.B.C. in order to have the "All Clear" signal given from Broadcasting House, as I am informed that a number of people in shelters were waiting for a signal from the B.B.C.?

Sir William Davison

May I ask my right hon. Friend whether he has considered the possibility, while having the signals which we have already been discussing, of some signal being given to the millions of people who have the telephone—the "All Clear" signal, at any rate?

Mr. Garro Jones

Can the right hon. Gentleman say whether proper principles have been worked out as to the magnitude and direction of a given threatened attack which will warrant a warning over a given area, particularly in view of the fact that one unidentified aircraft was held to justify the warning system given over half the British Isles?

Sir J. Anderson

That is rather a different question. My responsibility begins when communication of a prearranged kind is received from the Royal Air Force, but I do know that a very careful plan has been worked out, and it does provide for adjusting, in the light of experience, the areas over which warning is to be given, following the detection of aircraft in small numbers and in large numbers, as the case may be. To that I would only add that we have taken the view, for the present at any rate, that it is better to err on the side of safety. With regard to the other question put to me by my hon. Friends behind me, I can only say that every possible expedient will be considered, if experience should show that the existing system requires improvement?

Mr. Greenwood

Will the right hon. Gentleman keep to one form and not bring in other agencies, such as broadcasting and the telephone, because that multiplies the possibility of error of the human factor?

Sir J. Anderson

I assure the right hon. Gentleman that that is very much in mind.

Mr. Thorne

Can the right hon. Gentleman give any reason why the danger signal should not be as loud as the calling off signal?