There are a few options for you:
Gap year and reapply – this is a popular option and there are a lot of people who get into medical school at their second or even third attempt. One of the advantages to this is that you will already have your A level grades and can target your applications - and you have experience of doing BMAT/UCAT.
Do a different degree and apply as a graduate – while this is a good option for some, it does have MAJOR disadvantages. You'd need to get at least a 2:i in order to apply as a graduate. Its ludicrously competitive - even worse than 5 year Medicine. Financially it's difficult as well – although is Graduate entry its still an undergrad course and you wont get a second Student Loan, so unless you've got savings .....
Think very seriously about doing Medical Sciences instead. Many people get obsessed about 'being a Doctor' and don't realise that cutting edge research into disease, immunology and other areas like neuroscience, cancer biology, genetics, parasitology, immunology and even forensics, is often FAR more interesting and exciting than being a medic. It's where the future of medicine is being developed and discovered. Do you want to look at antibiotic resistance, research vaccines against SARS and Ebola, develop ground-breaking cancer treatments? Remember, doctors don't win Nobel Prizes - Medical Scientists do.
Did you get an Offer for your Fifth choice? Presumably you applied for this because it was an acceptable alternative to A100. (And if it wasn't, why on earth did you apply for it?). Go for it. Not everyone can become a doctor. As with the suggestion above about Medical Sciences, there are plenty of other areas of 'medicine' beyond actually being a doctor. The world also needs ambitious biochemists, pharmacologists and neuroscientists. You shouldn't regard this option as 'failure' - its simply working in a parallel area.