Yifan's heroes - that is the most ridiculous statement I have ever heard. apart from your facts of what you need being wrong, it is also a rather strange comment to say 'the medicine course of a "good" university' as gaining a post grad job as a doctor will most likely not be affected by the university you went to. to gain a medical degree is extremely universal - there is no classification of grades and to get into medicine you must have high grades anyway - i.e no one will be particularly stupid. the reason your friend got rejected with 4 A's is nothing to do with the fact he didn't have 5. in fact if you knew what you you were talkin about you would know that medical schools don't care if you have 300 A 's at A level; they want AAB/AAA. Most want you to gain those A's in two years but there are some exceptions, and also more exceptions for some one with extenuating circumstances. Your friend could have failed for many reasons - poor interview performance, poor personal statement, not enough work experience, lack of people skills, understanding, empathy etc, lack of passion or commitment for the subject, lack of many other things aside from his 4 A's.
To the OP: Maybe as mnay have said you should tell us your grades/ expected grades. Peninsula for example garuntee interviews to students who have taken a year out who already have AAB (even ABB if it is in the right subject requirements etc). If your heart is in medicine then you should at least spend one more year trying - you will have nothing to lost and could gain a lot from a gap year. You can reject your place for economics on results day if you decide you have the results to reapply, and if you dont have the grades but dont want to do economics then you can reapply to something else. Perhaps next year if you reapply put a place down as a back up - something that you could either take into post grad medicine or something that you could see yourself doing other than medicine. If you rush into taking this economics course and you aren't sure then it may become more difficult.