The point is that at the date of preparing the financial report...

The point is that at the date of preparing the financial report there is no guarantee that the sale will proceed because there is no signed binding contract.

But because the non-binding sale indicates that it is only worth whatever Aspen have offered, there is a shortfall between that amount and the amount on the books as the carrying value. That amount of difference has to be booked into the half yearly accounts as an expense.