This article is about the original A403 in West London that is now the A40. For current road between Avonmouth and the M48, see A403.
Western Avenue as it is today
The A403 was originally allocated to Western Avenue, a new major arterial route from White City (near the former BBC Studios) to Uxbridge, providing a bypass of the heavily built up A40 Uxbridge Road. It opened (in stages) with this number (the road did not exist at all in 1922), though eventually its importance over the parallel older road was recognised, and according to the relevant Ten Mile Road Maps it was renumbered to A40 between 1939 and 1946 (with the latter date being most likely for obvious reasons), with the old A40 Uxbridge Road becoming the A4020.