My opinion - It's a low value domain. The problem with it is that it's non-distinctive. Therefore, it cannot be used to market a forex business. Therefore, there is no reason for a business to want to acquire it.
The problem with the name is that it is a long generic meaning too long to "brand", and very forgettable.
So, forex.uk could be branded. Some value here.
forextradingsystem .uk - Too long to be branded and very generic and forgettable. You could say this name to someone one day, and the next day they will not remember you.
Good luck anyway!