If you've set your sights on getting an iPad rather than an iPad 2, then the cheapest new model we could find on the market comes from an online retailer which sells it for only £315 including delivery.
Simplyelectronics stocks the device for £319.95, £9 less than the discounted Apple price. But by using the voucher code SE5SAVOO, customers will be able to cut the price to a mere £314.95, a full £114 less than the full retail price of the iPad a few weeks ago, that's a 27 per cent savings; stocks are obviously limited and the price applies to the 16GB Wi-FI only model.
The older iPad is slower than the new one, has a much weaker graphics subsystem and costs £84 less than the iPad 2. It is also slightly thicker and heavier than the new one plus it doesn't come with the cameras.
The differences aside, there's not much that differentiates the two. The form factor is similar, ditto for the OS and more importantly, the form factor and the screen size and resolution.
If you don't mind buying refurbished products from Apple (which after all comes with full Apple warranty and new accessories and box), then keep looking at the dedicated Apple refurbished iPad page here for recertified stock which cost as little as £289 including shipping.