In the Great Britain road numbering scheme, the country is divided into numbered zones, the boundaries of which are usually defined by single-digit roads. The first digit of a road's number should be the number of the zone it occupies. If the road occupies multiple zones, then the furthest-anticlockwise zone is the correct one. The following tables list all British roads which are anomalously numbered. Roads in bold lie completely outside their "correct" zone; all other roads run for some length in their "correct" zones but trespass into zones anticlockwise of this zone. A further table lists duplicated road numbers.
Motorways The motorway zone boundaries are different from the A-road boundaries.
Road number Location Trespassed zone Reason M48 Gloucestershire, Monmouthshire Zone 5 This road used to be the M4, and as it lies to the north of the current M4 and to the west of the M5, it is in the Motorway Zone 5. M49 Bristol, Gloucestershire Zone 3 This motorway lies entirely within zone 3. The motorway was constructed at the same time as the Second Severn Crossing, and it is likely that the sequential M48 and M49 were used for the old M4 and the new motorway respectively. M62 Merseyside, Greater Manchester Zone 5 The section from Liverpool to Manchester was planned as M52, but was added to the M62 to make a cross-country route. M65 Lancashire Zone 5 The short link to the A582 is out of zone
While the M25 may appear to contradict these rules as it runs through all the London-bound zones, it in fact does not: it does not quite form a complete circle. It starts in Zone 2, south of the Thames, and proceeds clockwise through zones 3, 4 and 1. The A282, which completes the circle mostly formed by the M25, is anomalously numbered; as it proceeds into the A-road 1-zone (and should therefore begin with a 1).
The M271 is numbered as a spur of the M27, as opposed to the traditional numbering rules; however the M3 to Southampton came after the M271 was built and is not the zone boundary, which appears to be a straight line from M3 J8 to Exeter in some documentation.
A roads
Road number Location Trespassed zone(s) Reason A14 Northamptonshire Zone 5 & 6 The A14 was chosen as a unique, important number for this crucial cross-country route. A31 Surrey Zone 2 Formerly north-east of the A3 before the Guildford Bypass. A42 Leicestershire Zone 5 The A42 is numbered as an extension of the M42. A51 Warwickshire Zone 4 Extended over an orphaned section of the A423 when part of that road NW of Coventry was downgraded to B class. A55 Anglesey Zone 4 The A55 supersedes the A5 through Anglesey. A66 Cumbria Zone 5 The A66 was extended westwards beyond the A6 to make it a coast-to-coast route. A88 Falkirk Zone 9 Planned to extend westwards to form the A80 to Kincardine Bridge road - this instead became the M876. A89 Glasgow Zone 7 The A89 through Glasgow used to be partly the A8. A91 Stirling Zone 8 Rerouted to bypass Stirling. Meets the A9 at Greencornhills Roundabout yet continues into Zone 8 as far as the Bannockburn Interchange. A167 Durham Zone 6 The A167 through Durham used to be part of the A1. A168 North Yorkshire Zone 6 The A168 originally only went from Northallerton to Dishforth, and was extended by the former A1 when it was upgraded in 1994, changing the most westerly point to a different zone. A177 Durham Zone 6 In County Durham the original A1 route (now A167), not the A1(M) motorway, forms the zone boundary. A181 Durham Zone 6 In County Durham the original A1 route (now A167), not the A1(M) motorway, forms the zone boundary. A199 East Lothian Zone 6 The A199 used to be part of the A1. (With respect to the Scottish numbering hub of Edinburgh, the A199 is in fact correctly numbered as Zone 1 is anticlockwise from Zone 6 when viewed this way.) A282 Thurrock Zone 1 New road which is important and assigned an A2xx number as most A1xx numbers were already used (as zone 1 is far larger than zone 2). Could have been A108 or A122, both unused numbers at present. A307 Surrey Zone 2 The A307 used to be part of the A3. A320 Surrey Zone 2 Formerly north-east of the A3 before the Guildford Bypass. A322 Surrey Zone 2 Formerly north-east of the A3 before the Guildford Bypass. A397 Portsmouth Zone 2 The A397 used to be part of the A3. A404 Windsor and Maidenhead Zone 3 The A404 originally began on the A4 1.7 miles west of where it now passes under where the A404(M) passes under the A4 and loses its motorway status. The change in route took place in September 1992 when the A404 was rerouted and took over the what was previously the A423(M) which itself had originally been part of the M4. A412 Slough Zone 3 The A412 begins in Zone 3, at the A332. A427 Northamptonshire Zone 6 The A427 previously ran from Coventry to Oundle, and was truncated west of Market Harborough, when the new A14 opened. This section was renumbered as the B4027, A4303 and A4304. An even older alignment (pre-c.1960s) heading south from North Kilworth as far as the A45 is now an unclassified road (formerly B5414) and A4071. A447 Leicestershire Zone 5 Route south of the A47 decommissioned, leaving the remainder out-of-zone. A505 Bedfordshire Zone 4 The A505 was extended to become a cross-country route. A601 Derby Zone 5 Chosen as a unique number for the Derby inner ring road. A620 Nottinghamshire Zone 1 The A620 was truncated and left east of the A1. A624 Chapel-en-le-Frith, Derbyshire Zone 5 The A624 was part of the A6 for a short stretch in Chapel-en-le-Frith before the Chapel by-pass was built. A683 Lancashire Zone 5 The A683 was extended westwards to Heysham docks. A688 Durham Zone 1 Extended east of the A167 (former A1) in the 1980s. A689 Cumbria Zone 5 The A689 was extended south-westwards around Carlisle from M6 J44 to the A595 in the 5 zone. (It passes through the 7 zone as well between the A7 and River Eden, but the actual boundary between the 5 and 7 zones is undefined, and a road crossing the A7 would be correctly numbered starting 6, as zone 6 is anticlockwise of zone 7 as viewed from the numbering hub of Edinburgh.) A720 Edinburgh Zone 6 The A720 bypasses the numbering hub of Edinburgh, making numbering difficult; A720 was chosen for apparent importance. Most important 6-zone numbers were all used. Also notably distant from all other A72x roads. A882 Highland Zone 9 The A9 was rerouted to terminate at Scrabster rather than John O'Groats, leaving the A882 in zone 9. A899 West Lothian Zone 7 The A899 was extended south through Livingston new town, Scotland. A904 Falkirk Zone 8 The A9 was rerouted to bypass Falkirk town centre. A949 Highland Zone 8 The A949 used to be part of the A9. A1000 Hertfordshire Zone 6 The A1000 used to be part of the A1. A1057 Hertfordshire Zone 6 The A1057 used to be part of the A1. A1068 Northumberland Zone 6 The A1 was rerouted around Alnwick, leaving the end of A1068 out-of-zone. A1081 Hertfordshire Zone 6 The A1081 used to be part of the A6. A1246 North Yorkshire Zone 6 The A1246 used to be part of the A1. A3023 Hampshire Zone 2 The A3023 was originally the B2149. A3100 Surrey Zone 2 The A3100 used to be part of the A3. A3400 Warwickshire Zone 4 The road was numbered to reflect its history as the old A34. A4174 Bristol Zone 3 The A4174 is part of the Bristol outer ring road. It was entirely in zone 4 but has been extended to the A4 and then south of it. A4208 London Zone 3 Truncation of the A4 left the A4208 out-of-zone. A4300 Northamptonshire Zone 5 The A4300 used to be part of the A43. A4303 Leicestershire Zone 5 The A4303 used to be part of the A427. A4304 Leicestershire Zone 5 The A4304 used to be part of the A427. A4500 Northamptonshire Zone 5 The A4500 used to be part of the A45. A4501 Northamptonshire Zone 5 The A4501 used to be part of the A45. A5127 Staffordshire, West Midlands Zone 4 The A5127 was extended south when the A38 bypassed Sutton Coldfield. The entire A5127 was part of the original route of the A38. A5140 Bedfordshire Zone 4 Much of the route became A421 when it was extended, leaving only the section in Bedford, which is out-of-zone as it is east of the A6. A5153 Anglesey Zone 4 The A5153 lies south of the A5. A5154 Anglesey Zone 4 The A5154 used to be part of the A5. A5223 Telford Zone 4 Route begins south of the A5. A6004 Leicestershire Zone 5 The A6004 used to be part of the A6. A6010 Manchester Zone 5 The A6010 is part of the Manchester ring road. A6143 Manchester Zone 5 The A6143 was originally part of the A57. A6144 Trafford Zone 5 The A6144 used to be the B5166, B5311 and B5158. A6182 Doncaster Zone 1 The A1 was rerouted leaving the A6182 out-of-zone.
B roads