The term 'London TUBE' refers to the London Underground, a rapid transit system serving a large part of Greater London and parts of the adjacent counties of Buckinghamshire, Essex and Hertfordshire. The system is the oldest underground railway network in the world, with the first section opening in 1863. The solution to the crossword clue 'TELLY' is the five-letter word 'TUBE'. This is an appropriate answer as the London Underground is often referred to colloquially as the 'TUBE'.