Well... how old are you, for starters? If over the age of say 28, I doubt A-level grades are going to be the deciding factor on your application. If younger... then I guess it could make a difference (and almost certainly will do if you're looking at a top tier firm), but you could give it a shot anyway! Take what the HR department tells you with a pinch of salt and remember you're trying to sell yourself to the head-honcho, who will probably have a more balanced view of your application than a box-checking 19 yr old. Basically you have to ask yourself this: Am I credible?