moob:
Your rights are that you should take them back to the retailer for an exchange or refund. If someone bothered me at my work with such a trivial complaint, I'd show them the door (I work in EH).
I know it's all this compensation culture, as op I presume you would be expecting a voucher for reporting it. Like I say look very carefully dates are not always clearly displayed, they can be very difficult to spot, you would look quite foolish if this were the case, I have some tinned stuff and it's been right on the ridge of the tin.