I too am experiencing great delays with HMRC Inheritance Tax at the moment, both in Probate and trust matters.
In a trust, where the deceased life tenant was not domiciled in the UK and had no UK assets, I have been waiting since early October for a letter to confirm that the trust has no liability to inheritance tax. When I sent a reminder in January, I received a reply saying that HMRC were “looking at forms IHT100 and 400 in more detail” when in fact there was no Form IHT400 submitted, as there was no need for an English Grant in the deceased life tenant’s estate. I cannot understand why it is taking so long to deal with this relatively straightforward matter and can only assume that there is a staff shortage or a lack of staff with the necessary experience.
In Probate matters I have been waiting for over two months to receive the certificate for Probate IHT421 in three estates, two of which are well below the nil rate band but neither estate is excepted. The third is a taxable estate where the tax has been paid.