I've never understood it either. Could it be that the work scope temporarily impacts on the cargo hubs at Heathrow and they need to divert some of it elsewhere? The way the papers had it they would be building packages for the Runway 3 extension at PIK and flying them down as required, which sounded a bit of a crazy way of doing things.
Edit:- This release was from last June,
https://www.glasgowprestwick.com/gla...logistics-hub/