Is this value, the value of the property on the open market or the rebuild cost? For a modern house, the value of the property is likely to be more than the rebuild cost. For a period property, the rebuild cost will be significantly higher
Moo is correct...it is whatever figure your total cover is for. Which as you correctly point out, for a Listed Building could well be more than the cost of a modern rebuild.
But, bear in mind that the payout will require you to pay for site clearance (which in the event of total loss could be expensive), plans/professional fees and the rebuild. And at the end of it all, as someone else commented, you will not be able to afford to rebuild something close to what you currently have.