Tesco are now stocking all iPads and you can buy now and pay later if you take out a Tesco credit card. Prices are the same as Apple but you can at least spread the cost over 6 months with 0% interest.
Read the terms and conditions and do not to use the credit card for any other purchases during the 6 months. Be sure to pay it off within the 6 months as the interest rates will rise to 16.9%.
Tesco have WiFi and WiFi + 3g models.