(26 May 2022, 8:32 pm)TEN 6083 wrote Travelsure YJ10 OAE by kieron mathews, on Flickr

it appears that Travelsure have taken over the Alnwick to Berwick stretch of the X18 as Arriva have been terminating at Alnwick and going back to Newcastle.

Not correct, Travelsure are operating the summer extra journeys only. Arriva are still running X18, albeit very I frequently North of Alnwick.