I would see a GP first as they will act as an impartial medical professional on your behalf. But yes, this does mean finding a decent GP that understands your situation. Unfortunately, gynaecomastia is massively misunderstood by GPs and is often not taken seriously. But there are a stack of GPs that do understand how this condition has severe psychological consequences.
Your GP will have few grounds in which not to refer you to an endocrinologist (hormone specialist) to make sure that your conditions is not caused by abnormal hormone levels. If he or she does not refer you, ask for a second GP opinion which you are entitled to. A good argument to use against a GP that does not refer is this, "If my gynaecomastia is caused by a hormonal imbalance and I choose to have surgery, there is a real risk that the gynaecomastia could return. Given that fact, would it be wise for an endocrinologist to rule out some currently unknown hormonal cause?" In other words, if surgery does not 'cure' me of this, the buck ends with YOU!
In the unlikely event things go this far, come back to this forum and I will give you further direction.
Even if you decide to bypass your GP, Mr Levick - and any other surgeon for that matter is obliged to inform your GP of your surgery, unless you specifically request that you do not wish your GP to be informed.
I had all me pre-op consultations before seeing my GP. Before I committed to surgery, I went to see her, let her know what my intentions were and ask her if there was any reason why she thought it was a bad idea. I know my GP very well and she could see that I had researched the whole surgery thing to death and so I had her complete backing. It was only then that I made an appointment to go under the knife with Mr Levick.