As others have said, there are some medical schools which don't require biology. But if you gain a place, it will be harder as you'll be behind in biology - but not impossible. I do know a medical student with only AS biology, but we mostly have full A-levels in it.
So yes, you can apply - but it will be harder. It may be useful to mention in your personal statement that your decision for medicine was made later than most (but is still founded on a firm basis including work experience etc. and you're very keen) and so you didn't select biology A-level as you have and interest in all science. But since realising, you've done extra reading in biology (actually do this, perhaps do the AS course next year and drop further maths to lighten the load. Or could you drop Maths entirely and end up with a full A-level in Maths? If so, you could easily get two more full A-levels (Chem and Phys) and an AS, or even an A2 in biology as well if you push it. You'd have a lot of free time on the timetable.) But biology would better prepare you for medical school. It may be helpful to defer your application back a year whilst you gain work experience etc. to show you're committed - then your application will be stronger. Do speak to a careers advisor about this sort of stuff though, and most importantly, try to find out as soon as possible whether or not you do actually want to read medicine. It's a big commitment. The later you make the decision, the harder it will be for you, as many potential medical applicants have had a few years to prepare and get their applications looking good.