I had the same issue as well. I rang them up twice before I went down to the shop. They confirmed on the phone they had them in stock but when I got there, they refused to sell to me SIM free and gave me all sorts of excuse that they wouldn't be able to sell without contract. Unbelievably, they even told me to go & get it from others if I wanted a SIM free.
I then told the staff off as they completely wasted my time of travelling all the way into the town for all the excitement of hoping to pick one up. P4U staff haven't got a clue what's customer service and they're not properly trained as they all seem dodgy who would tell you any bull****.
As pointed out by other posters, they shouldn't be allowed to advertise and then fail to honour the sale even though they clearly have stocks. I hope the person who has got this down on a video report it to Advertising Standard Authority so that such thing is not happened again in the future.
All is not lost though as I've now found out that with O2 it is considerably cheaper - £130 saving. I won't be dealing with P4U again.