I believe that in 1837 Charles Wheatstone and William Fothergill Cooke built a two-kilometre copper connection between Euston and Chalk Farm along the railway, itself then newly laid – arguably the first practical telegraph.

A similar trial connection established on the Great Western Railway between Paddington and West Drayton two years later was extended to Slough in 1843
This was the one that became famous when it was used by the police to call ahead to apprehend a murderer who had got on the train hoping to make his escape, a story that did much to popularize the new medium.