Hi,
Most of the students that I helped attain entry into medicine had done 2-4 different types of work experience, but the only ones I recall who had done a prolonged period (like the 6 months you quote) were those who had done this during a gap year (including a year taken to resit A levels). In my experience, med school admissions teams look at the global picture rather than work experience or any other aspect of the applicant's credentials/suitability.
So a good overall record of GCSE results, work experience, BMT/UKCAT scores, personality/dedication/passion for subjects taken, PS, AS results when these were to hand, interview technique/performance - ALL taken together permit a decision to be made whether to place an offer.
In my view, you should try to balance out these various features, and ensure, as far as possible, that one or the other do not encroach upon the rest.
Hope this is useful.