Vaz,
FWIW I think you'd need to find a flight school THAT also does maintenance, not all do.
Don't know about planks, but for rotary you could try LHC at Redhill or Heliair at Wycombe. Alternatively look at the bigger companies that also have engineering - Premiair at Blackbushe or Harrods at Stansted are a couple of possibles (albeit not an exhaustive list).
Good luck
FW