you have to understand re: the royal mail.
If there are duties to be paid then legally for this country, the post office pays the full amount on your behalf as they have to deliver your parcel.
The charge of £8 covers the costs involved in this (could be £100's) and there will be a few thousand of these every day so that's a lot of money royal mail pay out daily.
If you decide you don't want the parcel and ignore the demand, then royal mail have to send it back.
thought that was reasonable.