No, it's not taken into account whatsoever by any medical school that i know of, and i e mailed several of them asking specifically about it. At interview you may be asked why you didn't get good enough A levels to go to a top uni, but i was just honest and said i was immature and demotivated as a 17 year old, and they accepted that quite happily.
The Oxford story above is the only case i've heard of where the uni attended has been picked out as a criteria for applicants.
The courses that want graduates from elite universities can already pick them out by putting high A level requirements on their GEP courses.