That might be due to restrictions on things regular companies/people can post in the UK. I used to work for $big_parcel_company and the list of things you weren't allowed to send was... interesting. Some made sense (bodily fluids for instance) some just seemed like old hangups (which possibly accounts for the hair in this case).
Hair is a fairly dangerous product; Lice, fleas, ticks, and other nasties that can spread disease like to nest in it. It's technically a body part, and I only say technically for the sake of argument; It is a body part. Most people are grossed out by fingernail clippings, which are pretty much the same thing (Primarily keratin).
Hair (and probably fingernails, were there a market for them) is relatively easy to clean compared to other body parts, but it is still a potential biohazard. Having regulations and restrictions around it makes sense - And I'm a die-hard libertarian saying this.
Correct me if I'm wrong, but aren't those parasites only to survive on live hair, because of the heat provided by the head the shelter provided by the hair?
UK: I ran into the thing about batteries when sending a phone back to supplier not so long ago. Strange, I had to show the Post Office counter lady the original packaging that had space for the battery cut out of the foam. After some discussion, I was allowed to send the phone back but with the battery in the phone.
