I thought we had civil servants and public workers. Still if the answer to 5d. is either "unson" or "nosnu" then "unison" is probably right. Seriously, is it only me who feels a bit hacked off when such obviously essential information as a directly related clue/answer is left out.
I agree all possible info should be given, when posting a request for help here, and perhaps I should have waited until Pezbuin came back with the answer to 5dn. However I have seen this particular clue before in one form or another where the name of the union is related to some form of being at one.