get some 'sticky stuff remover' get it from larger supermarkets and decent hardware shops for a couple of quid, lasts years per bottle, scratch into the sticker with something plastic so as to not damage paint underneath, then dab on and leave it a few minutes. It dissolves almost all glues in minutes leaving a mushy mess, more liquid and the residue will just wipe off.
get some 'sticky stuff remover' get it from larger supermarkets and decent hardware shops for a couple of quid, lasts years per bottle, scratch into the sticker with something plastic so as to not damage paint underneath, then dab on and leave it a few minutes. It dissolves almost all glues in minutes leaving a mushy mess, more liquid and the residue will just wipe off.