Thing is that mains plug fuses have to conform to stringent British Standards, and must at least bear the ASTA diamond
http://www.intertek.com/marks/asta/diamond/ .
Since this is subject to strict auditing and approvals, it is inevitable that any audiophile fuse to be fitted to a 13A plug is a re-labelled standard fuse, certainly if it has the ASTA diamond on the relabelling.
Now there is nothing against this, and companies supplying these fuses certainly incur costs relating to relabelling, and possibly in collaborating with fuse manufacturers to provide fuses with plated end caps - silver or rhodium are typical.
I'm agnostic, as you know, regarding the extent to which this makes any difference at all - hard science says that the electron motion shuffling back and forth is tiny. The main difference I believe relates to reducing the contact resistance to the mains plug, and prevent contact tarnishing (I've seen this big time in the old rubber plugs, to the extent that the plug melted).
Craig