Braces on nhs, over 18 + studentWatch
“NHS orthodontic treatment is free for people under the age of 18 with a clear health need for treatment. But because of high demand, there can be a long waiting list.
NHS orthodontic care isn't usually available for adults, but may be approved on a case-by-case basis if needed for health reasons.
A rating system known as the Index of Orthodontic Treatment Need (IOTN) is used to assess your eligibility for NHS treatment. The British Orthodontic Society's website has more information about the different grades used for the IOTN.
NHS treatment is available for grade 4 and grade 5 cases. Grade 3 cases are usually judged on an individual basis. Treatment may also be made available if the appearance of a person's teeth, jaw or face is of concern.”
TL;DR - so it’s going to depend on how severe your orthodontic problems are. They will have to be classified as a grade 4 or grade 5, or potentially a grade 3, for you to qualify for free NHS treatment.
You should note though that they’ll only treat you if you have good oral hygiene. If you already have tooth decay, they might not treat you.