It is not impossible. I left school with AABBCC and got a 2:2 in psych then a 2:1 in nursing. Currently applying for med in a really round about route. I had issues with depression growing up which impacted my studies and self esteem and it is now, as an adult I feel I am ready to pursue medicine. Coming from other areas also adds a level of maturity to the profession that medical schools look for.
If you are studying at uni at the moment I would suggest aim for a 1st (2:1 at least) and you are able to apply for Grad entry courses. Some courses in England are only 4 years and offer reduced fees (but are crazy competitive...just like all medicine really).
The up side to grad entry courses is they vet you based on GAMSAT score or UKCAT. I would advice start looking into studying for these as soon as possible. Most grad entry courses don't look at your school results at all. I have applied to SGUL, Nottingham, Exeter and Plymouth. Scottish Unis wouldn't touch me as I got a 2:2 in my first degree.
Start getting shadowing and other work experience under your belt as soon as you can and keep records of what you did and what you got from it. Get the placement to do you a short letter on letter headed paper too as some Unis ask for proof of work experience.