In the UK you need a National Insurance Number to work, either employed or self employed just different levels of contribution. This tax just allows access to the basic services, healthcare etc.. it is NOT THE SAME AS INCOME TAX ON SALARY...doesn't matter whom you work for, what sort of scheme, you need the NI number. I know of no airlines where staff don't have NI Numbers...The "oldest profession" is a different matter, these " workers" probably don't even " exist" in the records, cam in strapped to a pallet or cargo
