The RF Environment Generator at Boscombe Down is (or was) used to check that ‘equipment that is potentially susceptible to electro-magnetic influence produced by radio frequency environments is tested to ensure correct and safe operation’. This also covers ensuring electrically initiated explosives do not suffer false detonation and, for example, rotor bonding checks for helicopters.
Be assured the tests are comprehensive and the bar is set high. They cover the complete HF/VHF/UHF bands, plus microwave frequencies up to around 35GHz; by means of (e.g.) Low Level Sweeps and Bulk Current Injection, and can be carried out in the hangar or by a mobile unit.
The REG is (or was) a UK Strategic Asset.
If you need more information, I’m afraid you’ll have to ask MoD. Or you could pay QinetiQ to play with your equipment, but all that’ll achieve is a lengthy report recommending years of follow-on work!
This is not the same as TEMPEST testing.