In London you better off going to the Dior Outlet which is located near Oxford in a nearby town called Bicester, or for full price Dior just visit the Boutique on Sloane street, Harrods and Harvey Nics are close by who also stock Dior.
Selfridges is down oxford street carry Dior. Also the New Shopping Centre Westfield have a Dior boutique.
Good Luck.