So to elaborate: Intercalation can be either compulsory, optional but a guaranteed opportunity, or available via a competitive application process. It can be in third year, but it can also be in 4th year (UCL does that I think?) or variable within the med school. I would definitely look into this in detail, possibly including contacting the med schools if info is not on the websites, before applying.
You would graduate with some kind of medical science BSc with a degree grade (1st, 2.1 etc) and I would expect non-medical employers to treat it as similar to say a biology degree.
Applying to medicine when you have some small doubts is fine and natural. But it is a huge decision, with a demanding application that will mean you are less likely to go to the uni you want to versus applying for other subjects. Most medicine candidates have AAA+ and would be Oxbridge candidates if they were applying to any other subject. If you did decide you want to do medical research, then applying for medicine is generally not a good choice.