the motorway officers had been standing on the hard shoulder on the m5 in gloucesteshire at night after pulling over a driver , who they suspected was speeding .
they then spotted a caravan heading towards them in the dark and at the last minute spotted the nearside back window was open .
the caravan , which sped past the two traffic police officers with its back window open , circled , and almost decapitated them .
the two officers spotted that the caravan 's window was open with just seconds to spare and managed to dive out of the way .