Britain's clocks were set to London by the railways

Until the 1840s, each British town kept its own time by the sun. Train timetables made that impossible to live with, and the law followed decades later.

Before the railways, noon in a British town was when the sun stood highest over it. The sun crosses the country from east to west, so towns west of London reached noon later. Plymouth ran about 16 and a half minutes behind Greenwich, Liverpool about 12. Nobody minded. No journey was fast enough for a few minutes to matter.

Trains changed that. A timetable has to say when a train leaves each station, and with every station on its own clock, a schedule became a puzzle. One early line kept Liverpool time on the way to London and London time on the way back.

The Great Western Railway was the first to give up, in November 1840, running its whole timetable on London time: the time kept at the Royal Observatory in Greenwich. In 1847 the Railway Clearing House, which coordinated the companies, recommended that every station do the same.

Two minute hands

For a while, towns lived with both times. In Bristol, about ten minutes behind London, the clock on the Exchange was given a second minute hand, so people could read local time and railway time at a glance. Watchmakers sold the same idea to travellers. A watch made by Benjamin Lewis Vulliamy in 1847 has one hour hand and two minute hands: a gilt one for London, and a steel one set to wherever you happened to be.

Two things settled it. From 1852 the Royal Observatory's time signal travelled by telegraph to railway stations, so Greenwich time could be known exactly far from London. And towns found it easier to follow the trains than to argue with them. By 1855, by one count, 98 percent of towns and cities had switched.

The law came last. Greenwich Mean Time became the legal time of Great Britain only in 1880, when the Statutes (Definition of Time) Act received royal assent on 2 August. By then most public clocks had been following the trains for a generation.

It is easy to think of standard time as something governments decided. In Britain it began as a scheduling problem, solved by railway companies, and only later written down.