Firstly, have to confess I wasn't aware Hotspur (or Penman Engineering as they now seem to be known) existed in Dumfries! Looking through their website, it does seem perfectly reasonable - probably even likely - that they would be able to carry on producing uparmoured vehicles so long as they could get access to both the vehicles and the necessary raw materials. If you check their website they have a page on reroling / extension where it looks like they take a pretty beat up Land Rover and convert it into an armoured variant.
http://www.penman.co.uk/life-extension.html
As to who would be using them, if you go by the published material the Scottish Army controls all of Scotland, whereas I have the Dumfries area being effectively independent (and allied with Carlisle), but either way I could definitely see whoever controls Dumfries having a number of improvised armoured vehicles at their disposal.
Good call...cheers.