(1) Where, on or after 25 January 1984, under or in consequence of any disposition, property becomes subject to a discretionary trust, the trust is deemed, on -

(a) the date on which that property becomes or became subject to the discretionary trust,

(b) the date of death of the disponer, or

(c) where there are principal objects of the trust, the date on which there ceases to be a principal object of the trust who is -

(i) under the age of 25 years, where the property became subject to the trust on or after 25 January 1984 and before 31 January 1993, or

(ii) under the age of 21 years, where the property becomes or became subject to the trust on or after 31 January 1993,