CG37360 | Absolute entitlement: contingencies: date of absolute entitlement
From HM Revenue & Customs · Capital Gains Manual
Where settled property is due to pass absolutely to one or more beneficiaries on the happening of a contingency, such as the death or remarriage of a particular individual, the occasion of charge on the trustees under TCGA92/S71 (1) is the date upon which the contingency occurs, even though the trustees may have prior charges to meet.