I've just got to work, so same laptop, but different IP address and bought GA tickets for Monday at O2 (£128 for the pair). Red Zone sold out (very annoyed, if had been in the office today would have red zone tickets)
So problem was if you are using an O2 connection to buy tickets for an O2 gig it says sold out. Using a Virgin Media connection I could buy tickets!
Now just need to work out how to get a refund for the VIP package for Sunday nights (£952 for 2 tickets) which I bought because I thought was sold out, not realising it was O2 blocking their own customers!