In Oz, low flying fast jets are largely restricted to military fast jet corridors IOT avoid this problem. They are activated by notam and are restricted areas.
Near accidents still happen with private civil a/c ocasionally wandering into this airspace, either due to not reading NOTAMS or Nav errors. I believe it is a good system, however.
It goes the other way too. I was on the flight deck of an RAAF Herc, tac flying in the Blue Mountains (west of Sydney) when we popped over a ridge at 250' to find a Jet Ranger at our level only a few seconds ahead! (Class G-uncontrolled).
During a night airdrop operation in an RAAF Caribou in SE Queensland we were nearly cleaned up by two afterburning f-111s climbing out accross our nose. (military control zone).
I have also been in a Civil SAR aircraft at low level during a search in restricted vis, when we came head to head with an RAAF Orion at very close range. The Orion was at fault and removed from the area. (Search area controlled by an Airservices King Air).
I take it fast jet, low level ops are not restricted in the UK?