Seen recently here is that the Three network is offering the 8 GB iPad at 199 (plus 24 month contract paying 25 pounds/month).
"Three" is including 15 GB monthly data allowance.
They also offer PAYG options.
(Only mentioning it because I use "Three" with 15 GB allowance and had been puzzled that not all networks seemed ready to offer more generous amounts than 1 GB etc, despite charging significant fees).