The Hanger Lane gyratory has a fearsome reputation among London drivers, and this finish lies right next to it, between Ealing, Alperton and Park Royal. It is a sprawling roundabout system where the A40 Western Avenue meets the North Circular, with traffic lights, lanes and junctions that confuse even regulars. Keep your wits about you and know your exit before you arrive.
Ealing, to the south, likes to call itself the Queen of the Suburbs, a leafy district of Victorian houses, parks and a busy town centre. Its film studios are said to be the oldest continuously working studios in the world, and the Ealing comedies of the 1940s and 1950s made the name famous. Pitzhanger Manor, the country house that the architect John Soane designed for himself, has been beautifully restored and is open to visitors.
Park Royal, to the north-east, is one of the largest industrial estates in London, and for decades it was home to the Guinness brewery, which closed in 2005. The Grand Union Canal winds through it, and its towpath is a surprisingly peaceful route through the industrial landscape.
Coming back from the North Wessex Downs, the M4 or the A40 brings you into London, and the final stretch is a test of patience. Traffic is heavy, especially at rush hour, and the North Circular is often jammed.
Once off the gyratory, the world calms quickly. Ealing Green, with its old trees and the studio gates on one side, is a five-minute ride away and a far better place to end than a petrol forecourt, though there are plenty of those too.