The A1, also known as the Great North Road, is the longest numbered road in the United Kingdom, at 410 miles (660 km). It connects London, the capital of England, with Edinburgh, the capital of Scotland. The numbering system for A-roads, devised in the early 1920s, was based around patterns of roads radiating from two hubs at London and Edinburgh. The first number in the system, A1, was given to the most important part of that system: the road from London to Edinburgh, joining the two central points of the system and linking two of the UK's mainland capital cities. It passes through or near north London, Hatfield, Stevenage, Baldock, Biggleswade, Peterborough, Stamford, Grantham, Newark-on-Trent, Retford, Doncaster, Pontefract, York, Wetherby, Ripon, Darlington, Durham, Gateshead, Newcastle upon Tyne, Morpeth, Alnwick, Berwick-upon-Tweed, Dunbar, Haddington, Musselburgh, and east Edinburgh.
It was designated by the Ministry of Transport in 1921, and for much of its route it followed various branches of the historic Great North Road, the main deviation being between Boroughbridge and Darlington. The course of the A1 has changed where towns or villages have been bypassed, and where new alignments have taken a slightly different route. Between the North Circular Road in London and Morpeth in Northumberland, the road is a dual carriageway, several sections of which have been upgraded to motorway standard and designated A1(M). Between the M25 (near London) and the A720 (near Edinburgh) the road is part of the unsigned Euroroute E15 from Inverness to Algeciras.
