I was wrong in my previous answer. I have just checked the Boots website and in the FAQ section I found this:
If you choose letterbox delivery, your package will be posted through your letterbox. If for any reason your package won’t fit through your letterbox or if you choose signed for delivery and you’re not in when the delivery is made, a card will be put through your door with details of where to collect your package from. Remember if a signature is required it will need to be signed by someone aged 18 or over.
So a signature MAY be needed. Could be dependent on the type of drug in the delivery