Compare the UK and US Apple Store prices. Almost without exception, every product in Apple's lineup is priced 20% higher in the UK than in the US. No more, no less. The 20% markup is so uniform and universal that it is clearly by design. I see no reason why Apple would deviate from its UK pricing strategy for the iPad.
A 20% markup on US iPad prices would lead to:
16gb (wifi) - US$499 -> £394
32gb (wifi) - US$599 -> £474
64gb (wifi) - US$699 -> £553
16gb (3g) - US$629 -> £497
32gb (3g) - US$729 -> £576
64gb (3g) - US$829 -> £656
A 20% markup on US iPad prices would lead to:
16gb (wifi) - US$499 -> £394
32gb (wifi) - US$599 -> £474
64gb (wifi) - US$699 -> £553
16gb (3g) - US$629 -> £497
32gb (3g) - US$729 -> £576
64gb (3g) - US$829 -> £656