You have to pay the charge, and then send in the red form on the package, along with a photocopy of the auction page and a covering letter explaining that comics are zero vatable and duty exempt. Quote commodity code 4902900000. Wait six weeks. You should get your money back, minus the £8 charge that Parcelforce (or whichever carrier, but it's nearly always them) levies.
If the seller doesn't make it clear that the package contains old comics, the clerk at customs will assume the item is for commercial use, or a toy.
After experiencing this all too often (erroneous customs charges) and what with C & E making it more or less impossible to contact them, I suggest you write this statement to the seller every time you buy something from America, even if you've bought from him before.
"Please write "old books" or "used books" on the customs description and nothing else, thanks".
Works for me.