To get a degree in medicine:
If you mean in your question how long does it take to become a "doctor" or "MD" or have "Dr" in front of your name, well then it takes 4 years of college, and then 4 years of medical school. When you graduate you will be a doctor.
To first be able to get a degree in medicine, you need to complete your GCSE at A-C in all subjects.
Then you will need to take biology and chemistry at A level and AS level.
Then you need to take the medical degree at a University.
And then you have your degree. It will take you at least five years or more but it will be worth it! :D