Capital or trading receipt

[simpsonite]

Hi all,
My client owns a coal mine and was approached by a company to either lease it or buy it out right.
The company offered my client a payment of 60k in order to deal exclusively with them and not to talk with any other firms.

My client agreed to receiving the 60k in 3 annual payments of 20k per annum.
The first 20k was received but the company subsequently went bust!

So i am not entirely sure whether this payment woudl be deemed a trading receipt or capital?!
Or could it be argued in any capacity that it is a tax free captial gratuitous receipt?

Any thoughts much appreciated,

simpsonite