(26 Jan 2021, 9:10 pm)V514DFT wrote Yes but even if they were Newcastle based, then its still possible for them to slot on to the X21/X22 if a breakdown happened elsewhere on the route,and those were the only buses available

This never happened though?

The only time I remember Jesmond providing a bus for an Ashington route, outside of the examples below, was for a StreetLite on the X15 one evening. 

They'd only step in if there's significant disruption (such as ADL deciding to do rectification work on all the E400s in one day a few years back) or if the last bus failed to turn up. That was what I was told a few years ago, so the arrangements may not be in place anymore. Even then they manage to provide something better than 2 buses out of their whole fleet.