They were used on the 518 (now the X18 as stated in the second photo) for a period of time:
7455 YJ57BVF on 518 by
dbp dearingbuspix, on Flickr
Then they gained a more generic Coast&Castles branding (no branding for a specific route):
Arriva North East 7456 YJ57BVG by
Johnathon, on Flickr