Not aware of there being a list of persons or companies in the UK that provide a customisation service on either clubs or Headcovers but here goes for starters ...
CLUBS / PUTTERS
Chris Finch
Golf Irons UK
_golf_id_ : Tom Boucher (Instagram)
HEADCOVERS
Glam Golf
Hell For Leather Golf
VARIOUS
Custom Putters / Milling specialists
ID Golf (personalised grips)