Where a trust is created by deed of variation, the start date of the trust, for all reasons other than inheritance tax is the date of the deed.
Any class of beneficiary will be as at the date of the deed, and not as at the date of death. Whilst this may not often be relevant, if the variation is being used, say, in a “double death” situation - to ensure the trust accurately reflects the terms and beneficiaries applying on the second death the wording used must create the same beneficiaries, and not just repeat the wording from the later will (which could result in the class of beneficiaries including persons who have died between the 2 deaths, and excluding any who might otherwise have become beneficiaries by being, say, born or adopted between these two dates). Such a disparity could result in HMRC rejecting the application of s.142 IHTA 1984 and s.62(6) TCGA 1992.
Where a settlement is made and assets diverted to it by deed of variation, again, it is only for IHT purposes (if the appropriate declaration is made) that the trust is deemed to have commenced on the date of death. For all other purposes, it is the date of the settlement deed that is relevant.