The issue is that the economic future has changed dramtically - right now no-one knows by how much or in which direction and we probably won't be certain for 3-4 years
What we DO know is that the £-$ exchange rate has gone south significantly - this obviuosly impacts on what we can buy from the USA - unless Mr Boeing is willing to bet that the £ will be back at $ 1.50 when it comes to delivery......................