Strobe hazard beacons?

what is the law on using the amber strobe beacons as used by breakdown vehicles, I want to buy the magnetic based one but can't get information on the legal use, even police I've asked were unsure.
REASON:
After a near miss changing offiside wheel on my caravan in un-lit rural road. Hazards on and wearing flourescent jerking the idiot said he didn't see me or the warning triangle 100 ft back he run that over and broke it. As the site is world wide I'm in U.K