Nottinghamshire, particularly Newark. It's the classic Marshallian industrial district (or cluster) for the wargames industry, home to Games Workshop, Foundry, Warlord, North Star, Perry Miniatures and many others.
Both Partizans and Hammerhead every year, plus every event held at Warhammer World or Foundry (or Warlord Games, once their store/games centre opens). The Newark Irregulars' calendar also lists a number of game specific competition days throughout the year.
London is an hour and a half away by train for Salute and SELWG.