I must confess that I had always believed that where there is a prior life interest the closing of the class does not happen until the life interest ends. That may be correct but I suspect the answer is not as simple or certain as that.
Williams on Wills contains some discussion on the subject, and the following extracts may be relevant:
“Where it cannot be gathered, from the context and the circumstances of the case, what time is referred to for ascertaining a class, the court acts upon certain rules of construction, which have been framed for the convenience of the donees and of the administration of property, and have accordingly been called rules of convenience.1 They are admittedly not founded on any view of the testator’s intention,2 and are artificial.3 The rules both as to real and personal property are said to be founded on the presumption that only persons in being are intended to take.”
“First rule of convenience. A class1 is prima facie composed of those members (if any) existing ascertainable and capable of taking2 at the death of the testator,3 but where the period of distribution is at a later date, the class opens so as to let in all those members coming into existence before the period of distribution.4 Apart from the letting in of additional members, the postponement of the gift does not otherwise postpone the time of ascertainment of the class,5 and, on the one hand, persons who come into existence after the period of distribution are excluded,6 and, on the other hand, those in existence at the death of the testator take an immediate vested interest, so that, if they die before the date of distribution, their share passes to their personal representatives.7 Where, however, the gift is immediate, but at the death of the testator no member has yet come into existence, then all the members of the class who are born at any future time prima facie are intended to take under the gift.”
“The period of distribution. The period of distribution may be postponed either by some prior gift, or by the nature of the property given, or by the conditions of the gift.”
“Postponement by life interests. In cases where the gift is postponed to a life interest, the period of distribution is usually, but not necessarily, the determination of the life interest,1 …”
These appear to confirm my original belief but it seems clear that this is not necessarily always going to be the case, and much will depend on the intention of the testator, if that can be ascertained. The second rule of convenience relates to conditions such as age contingencies, which I gather are not relevant in this case.