Yes, the western blot would be the final answer. The cost is now $345. You would need to find someone in London who would draw your blood and spin it down and then you would need to ship it. The $345 includes the consult with me which is necessary to provide you with a lab requisition to get the test.
Given the sore on your penis, I would suggest that you obtain the blot so you can move on with your life with more clarity.