While it is not entirely evident which line the Royal family were taking, the red poles suggest it is the Central Line, which runs all the way from West Ruislip in the west to Epping in the east (that being the longest single journey one can take without change; a total of 34.1 miles). It passes through the likes of St Paul’s, Tottenham Court Road, Bank, Oxford Circus, Marble Arch and Notting Hill Gate