Basically, if someone's not happy with the award they received, they have access to an appeal. First, it will be reconsidered by DBS Veterans UK, and if they're not happy with that, it then goes to the first-tier tribunal. That would be made up of a legal person, a medical person, and an ex-military person.
The applicant can go to the appeal. Sometimes if they don't want to go to the appeal, it can be held in their absence. They will also have someone, usually from the Royal British Legion, or a solicitor acting pro bono, and they'll go along to the appeal hearing. Then the case would be discussed. Maybe the findings will be that they have the correct award, or it might be that the appeal finds that their award should be upgraded. That is to say, it will be considered by a legal judge, by someone from the medical profession, and also someone who used to serve and can understand all the ramifications of having been in the military.