The longest A Road
The longest road in the UK is the A1 which is 410 miles long and goes from London to Edinburgh. Over the years several sections of the A1 have been upgraded to a Motorway.
Video drive along the A1
The longest B Road
The longest B road in the UK is the B6318 which goes from Langholm to Heddon on the wall and is 61 miles long.
The longest motorway in the UK is the M6 which starts at junction 19 of the M1 which is near Rugby and goes all the way to Grentna in Scotland. The M6 has a total length of 232 miles.
Just for good measure the shortest road in the Uk is the A308(M) which goes for a total of 0.6 miles and goes from Junction 8/9 of the M4 and the A308.