H set up an inter vivos interest in possession trust for W with the nominal sum of £10. The trust terms gives W a life interest, then on her death, the trust becomes discretionary with the kids as beneficiaries.
H died a year later leaving a substantial amount of his estate for the trust.
My question is, when are the charges due? As the trust was inter vivos and not a will trust, is it subject to charges now as the value of the trust fund has just been substantiated, or is it exempt as it’s a spousal IIP and so is only chargeable when it becomes a discretionary trust upon W’s death?
Any advice would be appreciated! 
TIA
Hannah