Is it possible to get orthodontal (braces) treatment on the nhs?

Not likely. If you mean national health service, that organization doesn't make individual clinical decisions. They staff places like community health centers who have policies about individual clinical questions. The state via it's medicaid program has guidelines that may also come into play. If the underlying orthodontic problem is quite severe there may be options but esthetic tooth movement is unlikely.
Likely not. The nhs in the usa is provided by medicaid and a mandate of a particular state. It is unlikely they would approve orthodontia unless it is integral to the medical health of the patient. Nhs is the common acronym for public health care in the U.K., and from what i know, they will provide service to those under the age of 18. Hope this of some help.
Yes. If you're asking about medicaid (nhs), it is possible...But unlikely, unless a case can be made for a severe nutritional or develpmental deficiency that could be aided by orthodontics. The other problem would be finding an orthodontist who would be willing to do it for the poor rates dictated by medicaid.