Mr Willcox bought the Spitfire from the Air Ministry in 1955 for £150. It's value today is what £1M? Maybe more?

According to the Office for National Statistics composite price index, prices in 2019 are 2,501.91% higher than average prices throughout 1955. The pound experienced an average inflation rate of 5.22% per year during this period.

In other words, £150 in 1955 is equivalent in purchasing power to £3,902.86 in 2019

If only they'd realised!