United Kingdom Legal Time Standard (Hansard, 27 November 1996)

§ The Minister of State, Department of Trade and Industry (Lord Fraser of Carmyllie)
My Lords, the Interpretation Act 1978 provides that, subject to the Summer Time Act 1972, whenever an expression of time occurs in an Act of Parliament, subordinate legislation, deeds and other documents, the time referred to shall, unless it is otherwise specifically stated, be held to be Greenwich Mean Time.

§ Lord Tanlaw
My Lords, I thank the noble and learned Lord for his reply confirming that GMT is the legal timescale. Does he agree that GMT is synonymous with UTC—atomic time—at zero longitude, and that GMT can also be Universal Time or UT1—astronomical time—at zero longitude? Does he further agree that GMT can also be Mean Solar Time—GMST—on the 258 Greenwich meridian? Is he aware that after 150 years Greenwich Mean Time has been removed from the list of international timescales in the current Astronomical Almanac for the reason given on sheet B5 which is, and I quote: Greenwich Mean Time is ambiguous"? Would he therefore consider a much closer definition of Greenwich Mean Time to be necessary so that it can maintain its historical place among the world's timescales and so that the national timescale is one which is much more clearly defined than it is at the moment?

§ Lord Fraser of Carmyllie
My Lords, the temptation is to answer "yes". I fear, however, that the noble Lord deserves a slightly longer response than that. I regret to say that, scientifically, I do not agree with him that Greenwich Mean Time is the same as International Atomic Time. However, he will be reassured to know that, while it is not exactly identical with Co-ordinated Universal Time, Co-ordinated Universal Time is corrected to less than one second to ensure that they are more or less the same. For that reason we do not consider there is any necessity to adjust Greenwich Mean Time, which is not Greenwich Mean Time any more because it is not calculated on a mean—at noon. Such is the historical use of Greenwich Mean Time for the description that we do not consider there is any need to change that, although it is recognised that a number of other countries have shifted the legal base of their calculation of time to Co-ordinated Universal Time. I hope that is clear to the noble Lord. I cannot claim that it is clear to me.

§ Lord Howie of Troon
My Lords, is the Minister aware that I greatly welcome this Question from the noble Lord, Lord Tanlaw, because it was only a year or so ago that he was foremost among those supporting a subversive Motion to replace Greenwich Mean Time with Central European Time?

§ Lord Fraser of Carmyllie
My Lords, I do not welcome this question from the noble Lord. That is a rather different issue from whether we should move to Central European Time. As I understand it, the difficulty arises from the irregular elliptical course that the earth takes round the sun and for that time, and every now and again, there has to be some correction. That is made by resort to Co-ordinated Universal Time. There has been the introduction, which astonishes me, of some 29 leap seconds in our calendar since 1958.

§ Lord Renfrew of Kaimsthorn
My Lords, given the undoubted merits of Greenwich Mean Time, does my noble and learned friend agree that there is a case tor adhering to it in the summer months as well as in the winter months?

§ Lord Fraser of Carmyllie
My Lords, I hope that this question is not intended to lure me into a debate about the desirability of summer time or Central European Time. With that in mind I shall restrict myself to saying that we should maintain our use of Greenwich 259 Mean Time for legal purposes. Whether it is changed for practical purposes for summer time is a completely different issue.

§ Lord Haskel
My Lords, this is obviously an important matter for scientists, but perhaps a little less so than for lawyers. Is the Minister aware that it is obviously more complicated than simply adjusting the pennies on the balance wheel of Big Ben? Can he tell us who is responsible for atomic time catching up with solar time, and how is that agreed?

§ Lord Fraser of Carmyllie
My Lords, Co-ordinated Universal Time is calculated by using no fewer than 200 atomic clocks situated around the world in 50 countries. Then the calculation is made by the International Bureau of Weights and Measures. I wish to stress that although it is located in Paris, it has nothing to do with the European Union.

§ Lord Geddes
My Lords, while appreciating that my question may be slightly wide of the mark, can my noble and learned friend confirm to the House whether it is true that France is abandoning Central European Time in 1997? What is his opinion as to what that will do to the times as regards Europe and the United Kingdom?

§ Lord Fraser of Carmyllie
My Lords, that is going slightly wide of the Question. It is entirely a matter for France to make its own determination. To bring this back to the Question, I understand that in calculating what is its time it will have resort to Co-ordinated Universal Time.

§ Lord Tanlaw
My Lords, can the Minister clarify one point? I agree that there is a very small difference between UTC and Greenwich Mean Time and that it would normally not apply, except perhaps in the Millennium. Therefore, supposing that GMT is running more than half a second behind UTC, will the Millennium start at midnight, according to UTC, or will we have to wait to the nearest second for GMT to catch up with it? Will the first British citizen be born in the new era with "midnight" shown on his birth certificate and UTC or will it show one second after midnight according to GMT?

§ Lord Fraser of Carmyllie
My Lords, the difficulty at the moment is that I am not sure it can be accurately calculated whether or not at the point of the Millennium Greenwich Mean Time will be ahead or behind Co-ordinated Universal Time. The only confident assertion that I can make is that it will be 0.9 seconds one side of it.

§ Lord Elton
My Lords, having startled the House by saying that Greenwich Mean Time is no longer calculated on a mean, will my noble and learned friend tell us in the meantime what "mean" means?

§ Lord Fraser of Carmyllie
My Lords, it is not calculated on the mean. It was originally based on a hypothetical mean sun and that was abandoned in 1925. A different basis has been used since then. The calculation is made from midnight, which allows for more accurate astronomical calculations. It also allows for variations that occur when the sun is behind or ahead of time in February and November. I hope that that is a clear enough explanation.