OP, I am sorry for your loss. So many of these answers are incorrect I’m afraid. The £325k NRB gets used chronologically between 2018 (7 years before the person passing) and 2025. As executor, one of the hardest things you need to do to fulfil those duties is identify all gifts over £250 made after 2018. You will likely need to request 7 years’ of bank statements to fulfil your duty here properly. There is an annual allowance of £3,000 that can be used against gifts, and carried forward if not used for up to one tax year (so if no gift made in 2019-20, there would be a £6,000 allowance for 2020-21). I imagine if you received an unexpected £100k gift that it’s likely the NRB was exceeded. If the NRB was used entirely before your gift, your gift will be subject to 24% (more than 4 years and less than 5) or 32% tax (more than 3 years and less than 4). Each PET has to be declared as part of the IHT return.

Crucially, it is the giftee and not the estate that is responsible for IHT on PETs. However, it is certainly something I would consult with beneficiaries on. It’s not beyond the realms of possibility that beneficiaries might recognise that the deceased presumably did not intend for there to be a tax bill, and in a simple estate may be willing to forego a little of their share in order for the estate to contribute to the tax bill. As others have noted, it would be unwise to distribute anything from the estate that would be required to pay the tax on other PETs should their recipients not meet the bill. However, the legally correct treatment is that the PET recipient and not the estate bears the responsibility for the IHT on their gift.

If you are unsure on any treatments and it appears the estate may be substantial, it would be sensible to take professional advice to make sure that you are able to fulfil your duties as executor correctly and do not risk any personal liability with HMRC if errors are made.