UK State Pension Info
State pensions (US social security and UK state pensions) are covered under the tax treaty and are ONLY taxable in the country of residence. If you live in the US and get a UK state pension you need to fill out an HMRC US-Individual-2002 to claim relief from UK tax, along with an IRS form 8802 Residency Certification.
So now you will get your UK state pension with no UK tax withheld and you simply include it on line 16 of your 1040 and write something like "UK state social security pension" in the description, as it is taxed as an annuity.
The best bit of this at no point do you have to quote tax treaty Articles.
Info provided by BE member "Nun"