Duplicate packages are highly unusual, and in the vast majority of circumstances this second despatch email will relate to an out-of-stock or pre-order book you have previously purchased that has now become available. Please check your order confirmation email or your Bookshop.org account details to see whether this is the case.
If when you receive your parcel it does contain items surplus to those you have ordered, please get in touch with us at uk.support@bookshop.org and we'll be happy to assist.