Derby North would fall on a 4.43 swing (!?)
Boundary changes around Derby were quite radical; Derby South is now a constituency that fits the name (and it becomes bomb-proof Labour by my reckoning, don't know what Wells thinks), while Derby North would better be called Derby North West; it'll now stretch from Labour voting wards north of the city centre to the LibDem strongholds (in local politics at least) in the western side of the city. The Tories three best wards in the city are all removed to Mid Derbyshire.
I think it was a Labour plan.