Greenwich Mean Time has a fight on its hands. In 1972 much of the world began marking the passing hours by Universal Coordinated Time (UTC), which is based on the vibration of the caesium-133 atom. But ships and planes carried on navigating on Universal Time, or UT1, which is also popularly known as Greenwich Mean Time.

Time passed, which is its habit (though nobody seems able to say for certain why. Einstein suggested the only reason for time was so that everything didn't happen at once). But it didn't all pass at the same pace. That has spawned a problem.

Because UT1 defines a second as one-86,400th of one rotation of the Earth, and because the Earth's spin is slowing, UTC and GMT are slipping out of sync; albeit very slowly. To stop things getting out of hand, the International Telecommunications Union (ITU) adds a leap second to atomic time every few years (things getting out of hand, in this context, means the gulf between UTC and GMT widening to an hour over the course of 600 years). The next leap second will arrive at midnight on December 31.

This anomaly has become too much for many ITU members to stomach, especially now that ships and planes use GPS, which runs on a version of atomic time. They want this year's leap second to be almost the last, effectively robbing GMT of its status as a time zone.

Britain is fighting this proposal, being loath to redraft laws that refer to GMT. But some in Britain already have given up the fight. Big Ben, the speaking clock and the BBC radio pips all mark UTC rather than GMT. There is no time to lose. For if we do not fight now to save Greenwich Mean Time, we may not get a second chance.