Airwave is, as Rigga says, an emergency services radio network which covers most of the UK landmass. It's based on a Cellular structure (pretty much the same as GSM) and uses a Motorola TETRA infrastructure (TErrestrial TRunked Radio). The radio units are normally obtained from SEPURA, Motorola or Cleartone, SELEX and EADS(formerly Nokia). Most of the UK users have SEPURA or Motorola. It's not a simple matter of finding a VHF or UHF radio on the right band, they have to be dedicated TETRA radio's and set up for use on the UK TETRA network.
Best thing for your mate to do is ask the Helicopter people who manages their network access and contact them, it will probably be the Police/Fire/Ambulance. If he really wants the run-around, contact Airwave...