Q. Foreign exchange - Maximum loss?
From Marton's point of view an adverse outcome is depreciation of the dollar against sterling as this lowers its income when converted into sterling. The most awful outcome is thus an exchange rate of US$1.60:£1.
Presently its dollar income is £5m × 1.45 = $7.25m. At US$1.60:£1 its sterling income would fall to $7.25m/1.60 = £4.53m. Therefore the worst outcome is a loss (compared to the current rate) of (£0.47m).