You might get some NHS funding if you can prove that its impairing you. For example that it causes sleep apnea(you will need to get a check up during sleep), or that it is recessed enough that it causes you severe mental distress. Otherwise, you're looking into a 10-40k pounds in surgeries AFAIK. Ive no idea about your overal facial looks, but profile wise it will be a huge upgrade. Bear in mind that you will need to have your overbite corrected and teeth straightened prior to surgery.
Maybe you can take a loan from your parents, after all its their wonderful genes and lack of orthodontal care in your childhood.