Nvidia said $699 for the Founders Edition.
So that is around £580 with VAT. However,as noted by many UK sites,the UK price would be around £620 which is correct.
The £40 increase is the "cost of doing business in the UK tax" which we seem to have.
You only have to look at the cost of Adobe software products to see how much that can be!!
The added pricing on top of that is probably down to the different OEMs too,which add their own premiums.
This is why reference GTX980TI and Fury X cards were not the same price at launch IIRC.