I have since emailed them, and this was the reply.....
"Thank you for your email.
Please accept our apologies for any inconvenience caused.
Due to difficulties obtaining stock of titles from this distributor (Network
DVRAB) we currently have to list the titles as unavailable. It seems that with
this particular title some copies have became available and so could be
dispatched to you. Due to availability is still extremely limited, we are still
listing the titles as reserve only so as to avoid any disappointment or
frustration.
If you should have any queries please do let us know, we will be glad to assist
you."