I can't speak to UK schools and I don't know what O/Ls are. But, the quick answer is that it is not that simple and ultimately, it may not matter.
Getting into medical school is very costly, in both time and money (application fees, travel to interviews, etc.) If your friend tries to get into the "best" school and doesn't, your friend will have wasted a lot of time and money.
It is better to do research and get into the best medical school for the individual. A school that the applicant has a reasonable chance of getting into (for example, most state schools are more likely to take instate residents than out of state residents), that the school's teaching philosophy matches the way they learn, and the school has success getting their graduates into residencies the applicant is interested in. For example, if the applicant is interested in research or an academic career, Duke or Harvard may be a great choices (if they can get in). Otherwise, look for a school that has a combined MD/PhD program, many do. If the applicant wants to be a community doctor in their home town, find a school that graduates a lot of doctors with this goal in mind.
But, the bottom line is, where you get your medical degree may matter less in the long run than what you do with it after you have it. Bad doctors can come from the best schools and great doctors can come the lowest ranked schools.
What do they call the person that graduates last in their medical school class? Doctor!