Tax is only withheld on distributions like dividends.  Subject to your personal tax situation you will be credited for your tax paid in the US.  This rate is normally 15% (down from 30%) if you have a completed W8 form. See below for how we complete them on your behalf. 

For Individuals and minor accounts, we instantly generate a complete W8-BEN form on your behalf.   This means your withholding tax is reduced to 15% (from 30%).