The original Canberras all had a crew access door fitted in the fuselage 8 O'clock position with the pilot's seat offset to the left. The PR9, although a new-build, was based on the PR7 but with a modification to the B(I)8 nose. The latter was itself a modification of the original Canberra and although it incorporated a 'fighter' style cockpit, access was still gained through the side hatch and so the pilot's seat maintained this offset position. The modified nose for the PR9 incorporated an opening cockpit for access and dispensed with the side hatch. The rear navigator position was also dispensed with and a new navigator station built in front of the pilot. Navigator access was through the hinged nose! To have put the pilot exactly on the centreline would have necessitated a redesign of the flying controls and much of the cockpit.
It was hardly noticeable from a handling point of view, but did give a better view of the ground when using the port-facing oblique cameras.
The PR9 had a large space below and to the right of the pilot where the access door would have been. This became a great place to store baggage etc, but was covered with the sliding fuel panel. Not a good place to drop you map!