US taxes and UK child benefit/child tax credit

A suggestion, OP.  You could ask your local Citizens Advice Bureau for advice.  Although they probably wouldn't know the answer, they might well take steps to find out, since it concerns a taxfree benefit intended to be used wholly for the welfare of children.  And the CAB has contacts, and is better placed to find the right person within HMRC to talk to. 
https://www.citizensadvice.org.uk

There's a box where you can put in your postcode and find your local office.

This has nothing to do with HMRC so you will get no joy.
I have written to HMRC, IRS and a couple of politicians on both sides of the Atlantic about the taxation of UK tax free benefits by the IRS when paid to US citizens.......no response at all. ACA is probably your best bet, but they never get anywhere either.

Maybe a letter to a local MP might ignite some indignation and some UK news papers might be interested that the US can tax benefits that are supposed to be tax free in the UK.

..... an IRS agent based in the UK who was asked the question many times and by professionals far more knowledgeable than ....me.

+1

........ that the US can tax benefits that are supposed to be tax free in the UK.

There's always the argument (similar to one popular in Canada) that UK benefits come from the UK taxpayer via the UK Treasury. If US tax is paid on these UK benefits, theoretically, it would come from the benefit itself. Is it not, in fact, directly subverting funds from the UK taxpayer, meant to benefit solely UK persons who need the benefit, to a second country,.... for free, at the UK taxpayers cost?

This has nothing to do with HMRC so you will get no joy.
I have written to HMRC, IRS and a couple of politicians on both sides of the Atlantic about the taxation of UK tax free benefits by the IRS when paid to US citizens.......no response at all. ACA is probably your best bet, but they never get anywhere either.

That's why I suggest contacting the CAB.  They're more likely to be able to get an answer - even if the answer is not what one would wish.

Maybe a letter to a local MP might ignite some indignation and some UK news papers might be interested that the US can tax benefits that are supposed to be tax free in the UK.

Yes, maybe.  A US citizen residing in Scotland and being taxed on their child benefit might well get the attention of their local SNP MP.

There's always the argument (similar to one popular in Canada) that UK benefits come from the UK taxpayer via the UK Treasury. If US tax is paid on these UK benefits, theoretically, it would come from the benefit itself. Is it not, in fact, directly subverting funds from the UK taxpayer, meant to benefit solely UK persons who need the benefit, to a second country,.... for free, at the UK taxpayers cost?

That's the argument I made when I wrote to my MP and HMRC....that a foreign country was counteracting an internal UK government policy meant to aid it's residents and taking money from the UK Treasury.......no joy so far. The MP route is probably the best one and play up the interference in UK Governmental matters however indirect or tortured it might be.