There are set codes for procedures (called OPCS codes) that are considered fair and reasonable charges by the surgeon and anaesthetist. Not all of them stick to these rates, but the majority of them do. While there will also be regional variation for these charges, I am honestly surprised by the low fee Expat found (not saying it's not reasonable, but it does seem low). I would think the fees Meggles found are about right and I would expect that would cover pathology, too, but maybe not consultations or follow up. Not sure.
I'm not at work now, but if you want, I could find out what the OPCS charges are for this. From that you can at least have info to base your decision on if you go private (i.e. anyone who says it cheaper might need to be queried about what exactly is covered by their quote and vice versa). Knowing what the codes are is certainly a good way to make sure you don't get overcharged!