Cheers all! There are some interesting and subtle differences in the wording of all of those policies! See the quotes below, but some cover a far wider range of circumstances than others!
From Halifax/BOS policy:
you or your travelling companion is a
member of the Armed Forces, Police,
Ambulance, Fire or Nursing Service and
authorised leave is cancelled due to an
unexpected emergency or a posting overseas
at the time of your trip;
From Direct Travel:
You, your close relative or someone you are travelling with is a member of the Armed Forces, Police, Fire, Medical or Ambulance Services or an employee of a Government Department and has their leave withdrawn provided that the necessity to withdraw leave could not have been foreseen at the time of applying for insurance or booking your trip;