This discrepancy had mattered little in the days before railway travel but once rail networks began to create timetables covering the country it was soon clear that there was a requirement for  time to be standardised. 

In 1852, a telegraph line was competed linking Greenwich Observatory with London.  Shepherd's Electro-Magnetic Clock was installed at the Observatory specifically for the transmission of Greenwich Mean Time to distant places. The first transmissions were to London Bridge Station. Large, conspicuous clocks  began appearing at major railway stations so that travellers could be in no doubt that the trains on that line were running at what was known as "London Time". People had become very attached to their own "local" times however and for a long period many public clocks had two minute hands - one showing London (or more correctly, Greenwich, Time the other showing Local Time.

For reasons that varied from place to place, there was considerable delay in getting this simple idea accepted across the nation. There were many public meetings and much discussion in the local press before GMT became universally accepted in the UK. It was not until 1st June 1880 that the Definition of Time Bill, was read for the first time in the House of Commons. It received the Royal Assent on 2nd August 1880 and only then was there a "standard" time in use across the whole of Britain, removing all the confusion caused by local times.

Clocks on the Royal Estate at Sandringham only finally came into line in 1936, having been kept 30 minutes ahead  of GMT to allow King Edward VII more daylight time for shooting - his favourite sport.

From Trewman's Flying Post

28 Oct 1852

RAILWAY TIME

"It having been resolved at a Public meeting held at the Guildhall, Exeter on Thursday, the 28th day of October 1852:

"That it is in the opinion of this Meeting desirable that the Public Clocks in this City shall be set to Greenwich Time and the Right Worshipful the Mayor is requested to communicate with the authorities having charge of the principal Clocks with a view to the attainment of this object, at as early a period as may be consistent with giving the necessary Notice to the inhabitants."

"NOTICE IS HEREBY GIVEN:

That upon and after Tuesday the Second Day of November next, the Cathedral Clock and other public clocks of this City will be set to and indicate GREENWICH TIME."

Dated 28th October 1852.

Signed: William Willis Hooper, Mayor