It's your decision, but there's no harm in being open with the GP. Whether they approve or not, you'll still do what you think is best for you. They would probably be willing to assist and advise you. However, if you don't feel comfortable, it's your choice.
So, before starting your cycle, ask the GP for a full health assessment or hormone evaluation. You can request this without mentioning Anavar specifically. Then, about 6 weeks after your cycle, follow up with another blood test.