Scope: How much is chargeable: Contingent, uncertain or unascertained consideration: Definitions FA03/S51(3)
In relation to consideration
to be paid or provided only if some uncertain future event occurs or to cease to be paid or provided if some uncertain future event occurs
uncertain means amount or value depends on uncertain future events.
Where payment of an amount of consideration would be paid, provided a future event happens, then it should be assumed that event will happen and that amount will be paid.
Where an amount of consideration will cease to be payable provided a future event happens, then it should be assumed that event will not happen and that the amount will be paid.