Dear nun and sweetpeach
To take these in order:
1. Carrie is indeed a US citizen and taxable on worldwide income and gains in the United States. The reason why I said she could invest outside of the UK (eg offshore or back home in the US) and pay no tax at all was based on her facts and circumstances. She currently has her savings wrapped in a 401(k) and IRA. Her compensation once she is in the UK will lead to zero US tax because of the foreign earned income exclusion and foreign tax credits. The only income that might be taxable in the US would therefore be investment income that is not US tax sheltered. Assuming that she avoids PFICs any such income will almost certainly be covered by the annual exemption and the standard deduction. Hence zero US tax.
2. Jules is extremely unusual in being domiciled within the UK. The tests for changing domicile are very stringent, requiring relinquishing connections with ones previous domicile and acquiring similar connections with the new domicile. A leading tax case on this (from the beginning of the 20th century) related to a Canadian lady who was certain she would leave the UK and return to Canada if (and only if) her husband pre-deceased her. The Courts held that she was still domiciled within Canada. Similarly Jules may feel that if she was to be widowed and in need of comfort she would go home for comfort to family in the US. If so she is not domiciled here yet. Domicile is a highly complex subject and one of my specialties. The word does not have its ordinary English meaning when discussing tax.
If Jules acquired US mutual funds as a UK domiciliary and sold these any gain would NOT be taxed as capital gain. Instead it would be taxed here at up to 40%. The long-term US rate is however only 15% so the UK would want the difference (ie up to an extra 25%). If, having thought again, Jules is actually non-UK domiciled then the up to 40% UK tax would only apply if the gain was remitted to the UK.
3. The reason I said that many UK investments are not available because of SEC regulation is because the majority (maybe all?) UK mutual fund families will not handle US investors because the fund managers would have to comply with SEC filings. There is long-standing discussion on this topic; e.g.
http://www.sec.gov/rules/interp/33-7516.htm , and
http://www.law.duke.edu/journals/dltr/articles/2001dltr0007.htmlThe subject also features in articles in the Financial Times occasionally.
Neither Jules nor her husband should sensibly invest in collective investment products (such as unit trusts, investment trusts and OEICs -- whether or not wrapped in an ISA) because the US tax filing requirement is horrendous, and the US tax rate on sale could easily be greater than the profits made...
4. Deferred annuities are common domestically within the United States. There was a fashion to sell these offshore as well (aimed at US residents) some 2 to 5 years back. I would be very concerned about the personal portfolio bond rules in the UK these days (which charge a deemed 15% growth each year to UK tax) even if the personal portfolio bond rules are not in play. From a tax (not investment) perspective I wsould avoid these. If you want pure term life insurance (whole life), then do buy that in the States as it is far cheaper.
nun is lucky enough to have his own adviser so will be able to field questions at that person. Folks such as Jules and sweetpeach would also benefit from personal advice if they do not already have dual-qualified US/UK advisers.