OK, as US citizens not claiming the remittance basis (I guess all of us of normal means who are more-or-less permanently resident in the UK), we have a problem:
1. We cannot (or should not) own US mutual funds outside of a tax-deferred wrapper (such as a traditional or Roth IRA, 401(k) etc.) because HMRC will tax us punitively.
2. We cannot own UK unit trusts (=britspeak for mutual fund) outside of a tax deferred wrapper (such as an occupational or personal pension) because they will almost invariably be PFIC's which the IRS will tax punitively.
3. The IRS does not recognize an ISA as a pension for purposes of Article 17 of the treaty. Apparently, this is because the HMRC doesn't recognize an ISA as a pension either. Hence, a stocks-and-shares ISA is, at least theoretically, very dangerous for US citizens.
4. However!! The HMRC recognizes a ROTH IRA as a pension (see
http://www.hmrc.gov.uk/cnr/res-dom-faqs.htm#e ). This is, of course, logically inconsistent since an ISA and a ROTH IRA are practically identical in every way. I think the reason for this inconsistency is because the IRS explicitly refers to a ROTH IRA as a pension for purposes of Article 17 in the treaty notes (
http://www.ustreas.gov/offices/tax-policy/library/teus-uk.pdf).
5. Accordingly, we should be able to put money into a ROTH IRA and invest in US mutual funds and get the benefits that we would have if were UK (only) citizens who owned a stocks-and-shares ISA. The treaty protects us from HMRC if we own US mutual funds in the ROTH IRA.
6. Some of you have gotten the impression that only US-sourced earned income can be contributed to a ROTH IRA. THIS IS WRONG!! (see
http://www.irs.gov/pub/irs-pdf/p590.pdf). The confusion arises because you cannot contribute earned income that is part of the income you have excluded on 2555 (foreign earned income exclusion). If you earn less than $91400 and exclude it all, then you have no eligible income to contribute (but hold on, the solution follows..). If you earn more than $91400, then you will have earned income that is eligible for contribution (as long as your modified AGI is not over the limit). It doesn't matter if it is foreign!! Now, if you earn less than $91,400, what do you do? Simple: don't use the foreign earned income exclusion (form 2555); use the foreign tax credit (1116) instead. Then, all of your income is eligible and you will be able to contribute the max to your ROTH. Actually, the benefits of using 1116 are myriad...For example, you get additional child tax credits (I get $2000 a year just for passing go..) and you accumulate unused foreign tax credit. If you are within 10 years of retirement, you will seriously need the unused tax credits to offset the US tax liability on your UK-tax-free 25% lump sum distribution on your UK personal or occupational pension. Anyways, that's another thread..
7. The problem is that it seems to be hard to open a ROTH IRA without a US residential address. Wells Fargo was totally stupid (I'm trying to get them to change their rules but I doubt if I'll succeed). However, Fidelity had no problem (you just couldn't use the on-line form as it couldn't handle UK postcodes and the fact that you don't live in a state. However, the print-out form is fine.)
8. There one thing I'm not entirely clear about (and this is big..). As far as I can tell, HMRC is fine with not taxing gains from ROTH IRA's that have been opened after you establish residency here . Just for clarifcation: the same is not true with a traditional IRA where one is deducting contributions from taxable income. Such deductions from UK taxable income would only be allowed if the traditional IRA was established prior to arrival in the UK (see Article 18 of the treaty). Moreover, HMRC will tax distributions from a traditional IRA but not from a ROTH (again see
http://www.hmrc.gov.uk/cnr/res-dom-faqs.htm#e). Fair enough. The reason I'm a little paranoid about the ROTH situation is that the US/Canada tax treaty explicitly makes gains from contributions to Roth IRA's made by a US citizen after he has moved to Canada be taxable upon distribution. "The pension bifurcates(!) into two pensions.." However, it doesn't seem that the US/UK tax treaty has this problem. I've actually asked HMRC about this but I somehow doubt if I'll ever get an answer. I hope I haven't given them any clever ideas..
However, there is nothing in Article 17 that would allow the UK to do what Canada does in their treaty with the US.
Anyways, I'd be grateful any comments on all this. I'd also be interested to hear about experience people have had from various financial advisors and brokerage houses about opening ROTH IRA's from the UK.