Ok, as far as I know, they just want you to complete your A levels within the two years.
However one of my offers (Nottingham) specified no A2 resits and only one AS resit per subject so you might want to actually do your research.
Every university is different and asking 'Do medical school do...*this*?' is a bit futile seeing as they all have their own way of doing things.
But as I said, most of them are agreed on the whole 'Do it within two years and they won't mind'.