16. Pre-commencement instruments: period difficult to ascertain.

If an instrument specifies for the purposes of property limited in trust a perpetuity period by reference to the lives of persons in being when the instrument takes effect, the trustees believe that it is difficult or not reasonably practicable for them to ascertain whether the lives have ended and therefore whether the perpetuity period has ended, and they execute a deed stating that they so believe and that the relevant provision of the Perpetuities and Accumulations Act 20091 applies to the instrument, that provision will apply to the instrument2. If that provision applies to an instrument, the instrument