It is the side road at Hendon Central station that heads towards the East (and actually gets the shorter green than the unclassified road opposite). The A41 changes its name from Hendon Way to Watford Way at this junction.
The B551 quickly goes over the Northern Line and runs along Queen's Road until it meets the A502 Brent Street at a mini-roundabout by Brent Green, where it ends.
Originally the B551 started on the A5 in Colindale and ran southeast to Hendon Central station and onto its current route. Part of this was taken over by the A5088 Edgware bypass (since renumbered A41) in the late 1920s and the northern section has since been renumbered A5150, leaving the short section remaining.
At the eastern end the B551 originally ran along the south side of Brent Green, joining the A502 further east.