Do I need a customs declaration for sending a book from the US to the UK?

Hi there,

Someone wants to send me a book from the US (I live in the UK) but want me to sort the customs declaration. I assume there's a form I would need to fill in so that they can attach to the parcel?

I've had a quick google and I'm pretty lost. Do I have to complete a form? If so do you have a link to the specific one? Are there any other considerations I should be aware of?

Thanks