It seems to be the sort of price range we can expect according to industry sources, but so far Zavvi appears to be the only one putting a price to it. Other retail pre-orders are just reservations.
The "lowest price guaranteed" so if it turns out to be a little more than £400 then you will only be charged £399.99. Might be worth considering.does promise the
Other retailers have begun their own pre-order/reservation schemes for Xbox One.