Hello Priya! I advice you not to redo your A levels again as it will become too difficult to get into Medicine, and i don't see the point wasting another year trying to get into a better uni. Try and make due with what you have now. I had a look through the league tables (guardian and complete university guide) and it appears that Kingston is indeed better than Westminster (but do more research on environment and location to determine which one you should go to)
You can attempt graduate medicine while doing biomed but yes it is very competitive so consider other career paths if things don't go well.
If you want to talk PM me you know who i am (pri pri !)