Biomedical science vs medicneWatch
Biomedical science degrees are normally just general academic science degrees. Some of them used to be called things like "physiological sciences" before the term "biomedical science" became trendier. It is essentially a degree in (usually human) physiology primarily, with relevant supporting bioscience topics in cell and molecular biology and biochemistry and genetics etc. Professionally the term "biomedical scientist" is protected by the HCPC, however unlike medicine it is not a direct route to working as a BMS after doing a biomedical science course usually. For starters, many biomedical sciences degrees are not accredited by the IBMS, which is a requirement to work as a BMS (to have such an accredited degree). Any bioscience oriented course can in principle call itself a biomedical science degree.
If you want to become a physician, surgeon, GP, etc, you need to do a medical degree. If you want to study sciences, work in a lab, maybe work as a biomedical scientist in the NHS, or go on to do academic research in biomedical fields, then a biomedical sciences degree is probably more relevant (and for working as a BMS it is required to have an IBMS accredited degree, among other things). Note that you can go into academic research in biomedical areas with a medicine degree, but that is not the primary purpose of that degree (whereas in a sense it is of the biomedical science degree, as with the exception of working as a BMS it is not connected to any particular profession, and since most biomedical science degrees are not IBMS accredited much less providing the placements required for HCPC registration, most biomedical science graduates do not become BMS's).
In a very loose sense the difference between a biomedical science degree and a medicine degree is like that between a physics degree and an engineering degree (although the content of a BMS degree and the first few years of a medicine degree overlap a lot more than between physics and engineering degrees...). One is more about the scientific theory behind the applications in some professional context, while the other is more about those applications in professional contexts, to a point.