I've looked on there and all I can see are answers that suggest contacting the Inheritance Tax Team. I've submitted a question anyway and will report any answers. There's an old thread on this forum that comes to the conclusion that IRAs/401ks are excluded from UK IHT, but it makes no mention of designated beneficiaries or the structure of US pensions as it relates to why UK pensions fall outside of UK IHT, so I'm looking for something about that in an answer. There are a number of sources from what look like professional taxation specialists that just say "US pensions are exempt from UK IHT" which is worrying to me. My current belief is that US pensions, IRA 401k etc, are NOT excluded from UK IHT and if I return to the UK I will seek professional advice.