I expect this has been discussed before, but I am looking for a definitive reference that answers the question of whether or not the 25% tax free lump sum that a UK resident US taxpayer might take on retiring with a UK defined benefit pension scheme is or is not US taxable. It has been suggested to me that the savings clause in Article 1(4) of the UK-US Convention says that the US "by reason of citizenship *may* tax its citizens, as if this Convention had not come into effect", and that the word "may" leaves the IRS discretion, and thus that they may choose not tax such a lump sum (i.e. to not activate the savings clause.) One person tells me that they have been told by an IRS agent, after extensive telephone conversation, that such a lump sum from a final salary scheme will not be taxed by the US. The advice from the IRS agent was "If it is not taxable in the UK then it is not taxable in the US."
If the advice from that IRS agent is correct then it is good news. However, lump sums are mentioned in Article 17(2), which is a paragraph which is not excluded from the savings clause by Article 1(5). This is explained at the end of a page of HMRC advice:
http://www.hmrc.gov.uk/manuals/dtmanual/dt19876a.htm. I have heard of US persons in the UK shying away from taking a lump sum on retirement because of they believed US tax would be payable. Were they advised over-cautiously? What is the truth of the matter? Is it a grey area, such that some IRS enrolled agents do have their clients paying US tax on these pension lump sum payments, while others do not?