Thanks Dunedin for your well considered response.
To be pedantic, the savings clause allows a 'Contracting State', not just the US, to ignore many of its provisions. Both the US and UK are contracting states, but UK domestic law does not generally seek to tax its citizens resident abroad, while the US does. As a UK resident, the Treaty does apply to me insofar as the UK does not ignore its provisions. So, as you say, the UK taxes it under its domestic law, but gives a credit for US tax paid to the extent allowed in the treaty. What I would like to know is what that extent is.
The UK does allow a credit for foreign tax paid, and as far as the UK is concerned, that credit would be calculated on a foreign dividend under the provisions of Article 10. So it assumes that an amount of tax up to 15% has been paid on the dividend to the US and seeks to give a credit for that amount. Exanple calculations can be seen in the Explanatory memo under Article 24(6). Note that in Example 1, the US tax actually paid is 26%, not 15%, and with the 'Net post-credit U.K. tax' of 10%, the total tax is 36%, the same as the US rate ignoring the treaty. So the treaty does not limit the amount of total tax payable (in this case 36% according to US tax rates), but merely ensures that the total of US and UK tax adds up to no more than the 36% the US would tax without the treaty intervention.
However, in the case of the Bond dividend, the UK taxes it as if it were interest, i.e., at the rate applicable to interest, and it has to be put in the interest income box. But, does it still remain a dividend for tax credit purposes and subject to the procedure shown in Article 24(6) as a dividend? The explanation to Article 11 says 'Notwithstanding the foregoing limitations on source country taxation of interest, the saving clause of paragraph 4 of Article 1 (General Scope) permits the United States to tax its residents and citizens, subject to the special foreign tax credit rules of paragraph 6 of Article 24 (Relief from Double Taxation), as if the Convention had not come into force.' i am wondering how to apply these rules, i.e., in the worked example, would you use a witholding rate of 15% for dividends, or 0% for interest, and do i have to re-source this income and invoke the treaty on Form ? In fact, the payer of the bond dividend has not witheld anything, in recognition of the fact that I am a W8-BEN weilding UK resident.
Sale of the Bond Fund is another matter for another year. Sigh !