I have been through a complaints procedure with the RCVS. My advice would be to document everything as you go along so that it is easier to recall if you decide to go ahead with a formal complaint.
The first step is to meet with the Clinical Director, which I know you are doing. One of the sections on the form asks whether you have met to discuss the issues and whether anything was resolved.
I was acting on behalf of a rescue. I met with the Clinical Director on my own, but in hindsight it would have been less stressful if I had arranged for someone to go with me, if only for moral support and as a witness. I took notes in with me to act as a memory aid, I didn't want to forget anything. I made notes of what had been said/discussed as soon as I got out of there, while it was still fresh in my mind, again this helped when completing the complaints form. The Clinical Director later lied through his teeth about what was said....hence my regret about not having someone with me as a witness.
I requested full clinical notes from the offending practice. I think you have said that there are also xrays, so a copy of these would be brilliant to have.
I also had clinical notes from my vets, who had to do emergency procedures to save the two rabbits' lives. The rescue's ex-vet failed very badly, they were given an opportunity to correct their surgical errors, but discharged the rabbits the following day in the same appalling and infected state, so we had no alternative but to make a quick decision and get them urgently to my vet, for one of the rabbits in particular it really was life or death.
We had graphic photos, of the mess the first vet made and then some more photos after corrective surgery had been performed by my vet.
I hope your meeting with the Clinical Director goes OK, it's not a nice thing to have to go through.
If you think I can be of any further help, please let me know.