score:5
A quick browse through the imperial war museum collection suggests that ties were relatively common.
This picture shows two pilots with ties and one with some sort of scarf (which could be hiding a tie underneath) https://www.iwm.org.uk/collections/item/object/205452816
https://www.iwm.org.uk/collections/item/object/205446953 shows a Canadian pilot with a tie.
Just for good measure this photo shows 3 polo necks and two ties https://www.iwm.org.uk/collections/item/object/205209999
So in terms of the book picture I would say it's fine but I'm struggling to find proper combat pictures with ties visible there is a few "scramble" pictures for example https://www.iwm.org.uk/collections/item/object/205447273 but I'm not sure how many were just for the camera.