If you are prepared to finish the year, you won't have to go home. You can apply through UCAS whilst you are doing your current degree. I suggest you talk to your course tutor, explain that you don't enjoy chemistry and you want to do another degree. If you want to stay at your current university then it may even be possible to transfer internally. Also ask if you will be awarded a CertHE if you leave after the first year.
You should be aware however that this is your last chance. If you drop out again, you won't get another full student loan, so you must be sure that medical biochem is the right degree for you.