Railway maintenance equipment

[coq au vin]

Hello all, I do hope my question isn’t too OT for this forum, however late at night I have been watching a Class 66, followed by lots of fairly unknown equipment lit up with blue lights in trail. This is on the borderlands line where there is work ongoing. Google searches haven’t shown what I might be seeing…

Where are the works based for this track maintenance, and what equipment am I hearing pass by my home?

Cheers