Resurrecting this old post only because of my own research.
@durhamlad - I note your last post, but saw this today when trawling the HMRC website:
https://www.gov.uk/government/publications/pension-tax-for-overseas-pensions/pension-tax-for-overseas-pensionsChanges to taxation of pension paymentsCurrently only 90% of a foreign pension or annuity payable to a UK resident (except those claiming the remittance basis) is chargeable to UK tax.
For individuals who aren’t UK domiciled and are claiming the remittance basis, the amount of foreign pension or annuity chargeable to tax is the amount remitted to the UK.
Guidance on the current tax treatment of foreign pensions can be found in the Employment Income Manual at EIM74500.
From 6 April 2017 the whole foreign pension or annuity payable to a UK resident will be chargeable to tax. This means that pensions paid to UK residents will be taxed in the same way whether the scheme is based in the UK or overseas.
This change doesn’t affect the taxation of:
foreign pensions or annuities paid to non-domiciled individuals claiming the remittance basis
certain pensions paid following the death of a member or a beneficiary aged under 75, which will remain tax free
I presume that on this basis 100% of US Social Security is taxable in the UK - irrespective of whether or not is is remitted to the UK?
While the same Social Security is non-taxable in the US (by virtue of the Treaty), are there alternative treatments available here? for example, declaring it as income and taking the FTC from the UK tax paid? Would this then allow an accumulation of c/fwd FTC's that could potentially be used in the future if the USC/UK citizen decides to move back to the US - and then applied against UK pensions received in the US?