All UK AME's are also required to be registered I believe, as a professional with the UK GMC - with that in mind and if unable to resolve at a personal or clinic level - then a complaint can be considered/registered using the link below.
https://www.gmc-uk.org/professional-...ng-on-concerns
Although very rare, there seem to be still one or two AME's that have personality traits not conducive to the role they are undertaking. Be aware (IMHO) of ones that like to "refer you to my good friend Dr. XYZABC" for further medical investigative matters that they deem as required - a 'red flag' moment personally if that comes up! referrals are of course required and necessary at times but it is a case of 'buyer beware!', and you have the freedom to ask for a second opinion etc. Luckily I have a brilliant AME now and an excellent AME is worth their weight in gold.
Of consideration (and admittedly I've not done this myself) a friend in the past suggested - when considering a new AME it's always worth asking to book an appointment to essentially 'interview' them for the role as your chosen service provider (and it is a 'service' remember, regardless of medical requirements!). There are plenty of UK AME's to choose from and you are the paying customer, whether approved AME, or even the (UK) CAA.