If the inheritance tax on lifetime gifts is to be paid from the estate there would normally be an express provision to that effect. You haven’t stated the full wording from the will, but the fact you are unsure leads me to believe there is no contrary intention stated.
I don’t think the executors have the ability to pursue the lifetime recipient for the tax as such. There is nothing to this effect in the Inheritance Tax Act. If the tax is unpaid after 12 months the executors are jointly liable for it and HMRC are at liberty to pursue the executors. HMRC’s manuals state that they will pursue the donee if they can, and will not look to the executors merely because they are a soft option, but I think all the executors can do is encourage HMRC to pursue the donee and keep sufficient funds in reserve in case HMRC are ultimately unable to get the funds from the donee. That might happen if the donee is declared bankrupt, or lives outside the UK, etc.
Paul Davies
Clarke Willmott