A1 LONDON to EDINBURGH

A2 LONDON to DOVER

A3 LONDON to PORTSMOUTH

A4 LONDON to BRISTOL

A5 LONDON to HOLYHEAD

A6 LONDON to CARLISLE

A7 EDINBURGH to CARLISLE

A8 EDINBURGH to GLASGOW

A9 EDINBURGH to JOHN O' GROATS

Roads between A1 & A2 start with 1

Roads between A2 & A3 start with 2

Roads between A3 & A4 start with 3

Roads between A4 & A5 start with 4

Roads between A5 & A6 start with 5

Roads between A6 / A7 & A1 start with 6

Roads between A7 & A8 start with 7

Roads between A8 & A9 start with 8

Roads between A9 & A1 start with 9

e.g. The A17 runs from King's Lynn to Newark-on-Trent where it meets the A1,

the road which continues from this point to Chesterfield is numbered A617.

( Some long trunk roads do break the rule! )