M26 motorway the M26 at that time formed part of Ringway 4 and would have been designated as part of the M25. Construction of the first part of the M25 began in 1972 but before it opened, plans for the "London Orbital" motorway were modified to combine the southern and western part of Ringway 4 with the northern and eastern part of Ringway 3. To connect the two separate routes, which together were numbered as the M25, an additional section of road needed to be planned and the M25 route was diverted northwards from junction 5 to meet Ringway 3 at Swanley
London to amalgamate the city with its suburbs, causing "London" to be defined in a number of ways for different purposes. Forty per cent of Greater London is covered by the London post town, within which 'LONDON' forms part of postal addresses. The London telephone area code (020) covers a larger area, similar in size to Greater London, although some outer districts are excluded and some places just outside are included. The Greater London boundary has been aligned to the M25 motorway in places. Outward urban expansion is now prevented by the Metropolitan Green Belt, although the built-up area extends beyond