Your alpha preorders are worthless; I doubt anyone would take it for free, let alone give you any money for it.  Just the remaining balance alone, ignoring having to pay you for the deposit, is 1000 pounds and the miner is what, 10 weeks minimum from shipping if it ever even ships at all?  For 1000 pounds one can get the same hash delivered TODAY.
My suggestion would be to take them up on the refund offer.  50% is better then 0%.