This excerpt taken from the ICI 6-K filed Mar 21, 2007.
Taxation of capital gains for US resident shareholders
Under the Convention, each contracting state may, in general, tax capital gains in accordance with the provisions of its domestic law. Under present UK law, individuals who are neither resident nor ordinarily resident in the UK, and companies which are not resident in the UK, generally will not be liable to UK tax on capital gains made on the disposal of their Ordinary Shares or ADSs, unless such Ordinary Shares or ADSs are held in connection with a trade, profession or vocation carried on in the UK through a branch or agency.
A US resident shareholder will recognise capital gain or loss for US federal income tax purposes on the sale or exchange of the Ordinary Shares or ADSs in the same manner as on the sale or exchange of any other shares held as capital assets. Any gain or loss will generally
be US source capital gain or loss, which will be long-term if the Ordinary Shares or ADSs were held for longer than one year.