Welcome to our SCLS Community!
While I'm not knowledgeable with how to navigate Britain's NHS, and I hope you will also hear from the couple of our members who are also British, here is some generic advice:
1) You don't need out-of-area treatment for SCLS, so it's better to ask for what you really need, which is a senior anchor physician who is a specialist in internal medicine and is affiliated with a major trauma center (hospital).
2) Print out for your GP the contents of the sections in this site titled "Disorder Details" and "Disorder Resources"; then read and learn the contents; and then go over it with your GP and with every other physician or nurse that you ever encounter, so they will understand the gravity of your diagnosis and the life- and limb-saving options available.
3) Request a 2nd opinion on your diagnosis from a major medical center or, preferably, with physicians who are teaching and doing research at a nearby medical school. (Diagnostic mistakes are terribly common in medicine.) This might bring you into contact with physicians who are better informed and more compassionate.
4) Request an in-area referral to a hematologist and/or an immunologist. After all, SCLS is a hematological disorder, and the standard of preventive care involves the monthly infusion of immunoglobulins.
Please fill out the profile page with as many details of your medical history as possible, because we are still learning about SCLS, and keep us updated of your progress!