This excerpt taken from the ICI 6-K filed Mar 21, 2007.
Taxation of dividends paid to US resident shareholders
The UK does not currently impose a withholding tax on dividends paid by a UK company, such as the Company.
Distributions paid by the Company to a US resident shareholder will be treated for US federal income tax purposes as foreign source ordinary dividend income to the extent of the Companys current or accumulated earnings and profits for US federal income tax purposes. The amount of the dividend will be the US dollar value of the pounds Sterling received on the date the dividend is received by the Depository for US resident shareholders of ADSs (or in the case of Ordinary Shares, received by the US resident shareholder), regardless of whether or not the dividend is converted into US dollars. No deduction for dividends received is allowed for corporate US resident shareholders with respect to dividends paid by the Company. If the dividend is converted into US dollars on the date of receipt, you generally should not be required to recognise foreign currency gain or loss in respect of the dividend income. You may have foreign currency gain or loss if the amount of such dividend is not converted into US dollars on the date of its receipt.
Subject to applicable limitations that may vary depending upon a US resident shareholders individual circumstances and the discussion above regarding concerns expressed by the US Treasury, dividends paid to non-corporate US resident shareholders in taxable years beginning before 1 January 2011 will be taxable at a maximum tax rate of 15%. Non-corporate US resident shareholders should consult their own tax advisers to determine whether they are subject to any special rules that limit their ability to be taxed at this favourable rate.