I really can't see the UK price for the 64GB being more than £600. Just compare prices on the Apple store - US vs UK. Must items coming into the UK are subject to vat and duty, which combined is usually about 22% on there abouts - I used to buy a lot of Guitars from the US.
Check out the new MBPs for example. The UK price for my wifes 17" MBP is 22% more than the US model, plus about £30. iPods are similar, as is most of the product line. I don't see why the iPad won't follow the same logic too. So that's put the 64GB model at £599, assuming a crap exchange rate of 1.5.
This is all that's holding me off importing. At £650 for a 64GB model, plus 22% taxes you are looking at almost £200 more than the very likely UK price. I just can't justify that expense to get it two weeks early. Ironically, for the first time in ages, I could afford to splurge, but I'm keeping my head.