The A1 is the longest numbered road in the UK, at 410 miles (660 km). It connects London, the capital of England, with Edinburgh, the capital of Scotland. It passes through or near North London, Hatfield, Welwyn Garden City, Stevenage, Baldock, Letchworth Garden City, Huntingdon, Peterborough, Stamford, Grantham, Newark-on-Trent, Retford, Doncaster, York, Ripon, Darlington, Durham, Sunderland, Gateshead, Newcastle upon Tyne, Alnwick and Berwick-upon-Tweed.
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. Several sections of the route have been upgraded to motorway standard and designated A1(M). Between the M25 (near London) and the A696 (near Newcastle upon Tyne) the road has been designated as part of the unsigned Euroroute E15 from Inverness to Algeciras.
The A1 is the latest in a series of routes north from London to York and beyond. It was designated in 1921 by the Ministry of Transport under the Great Britain road numbering scheme. The earliest documented northern routes are the roads created by the Romans during the period from AD 43 to AD 410, which consisted of several itinera (plural of iter) recorded in the Antonine Itinerary. A combination of these were used by the Anglo-Saxons as the route from London to York, and together became known as Ermine Street. Ermine Street later became known as the Old North Road. Part of this route in London is followed by the current A10. By the 12th century, because of flooding and damage by traffic, an alternative route out of London was found through Muswell Hill, and became part of the Great North Road. A turnpike road, New North Road and Canonbury Road (A1200 road), was constructed in 1812 linking the start of the Old North Road around Shoreditch with the Great North Road at Highbury Corner. While the route of the A1 outside London mainly follows the Great North Road route used by mail coaches between London and Edinburgh, within London the coaching route is only followed through Islington.
Bypasses were built around Barnet and Hatfield in 1927, but it was not until c.1954 that they were renumbered A1. In the 1930s bypasses were added around Chester-le-Street and Durham and the Ferryhill Cut was dug. In 1960 Stamford, Biggleswade and Doncaster were bypassed, as were Retford in 1961 and St Neots in 1971. Baldock was bypassed in July 1967. During the early 1970s plans to widen the A1 along Archway Road in London were abandoned after considerable opposition and four public inquiries during which road protesters disrupted proceedings. The scheme was finally dropped in 1990. The Hatfield cut-and-cover was opened in 1986.
A proposal to upgrade the whole of the A1 to motorway status was investigated by the Government in 1989 but was dropped in 1995, along with many other schemes, in response to road protests against other road schemes (including the Newbury Bypass and the M3 extension through Twyford Down).