Royal Mail will allow you to input customs data where an item has zero value.One might be led to thinking that if a product is a gift or has no intrinsic value because it's expired, etcetera, then this would be okay.

Irish Post reject instantly any item which contains a value under one euro.. I have confirmed this with Irish Customs and it's taken nearly a year.

I have literally lost a thousand pounds worth of postage because of this error.