If you're over the age of 19 (or especially over 21) you may want to consider an Access to Medicine course. There are a number around the country, however not all are necessarily accepted by all medical schools - most have a number that they will accept from, and usually these are stated on their websites, but you ought to contact them directly to see if the specific Access course you're looking at is acceptable to make sure.
Otherwise you can take A-levels, however it may be costly, especially when you take into account the Science Practical Endorsements. There are a few 6 year medical courses with a foundation for "subject changer" students who have medicine level grades but in non-science subjects I believe - however check carefully as most such 6 year courses are for widening access students.