Many thanks. It was bought from ebay which did have a generic note saying there may be taxes I would be liable for certain items, but never had any before and assumed the £25 postage I was paying would be sufficient for clothing. Certainly didn't say anything about clearance fees.
I've had nothing to suggest the seller was aware I'd be paying extra charges, although don't really want to end up in a dispute with them, my beef is with parcelforce.