What I've noticed here in suburban Birmingham is that the postman DOES have the parcel with him if it's not too big...our regular postman now knows my husband (who is a nurse, so is home at interesting hours, depending on his shift) and has asked him if it's ok to leave stuff with the neighbours or put it through the letter box if no one answers - not a problem! As a matter of fact, if he leaves stuff with the neighbours, he notes on the card which house it's at and puts the card through the door. I call THAT good service!
If we have a larger parcel, that invariably comes to us through some other service (like Parcel Force which is, I think, run by Royal Mail?). According to my DH, they definitely knock on the door (obviously, if he's home, he has heard them). They do NOT leave parcels with the neighbours, but put the card through the door and we go to the sorting office to pick up.
So far, in the 18 months we've lived in this neighbourhood, we haven't ordered anything that we really feel the need to be home for, it just happens that due to his nursing shifts, he is sometimes home to await anything we've ordered. I've only had to await one visa by post, and I used my work address for that one...