I read in "Double Taxation Relief (United States of America) Order 1983"
"Article 14
Independent Personal Services
Income derived by an individual who is a resident of a Contracting State from the performance of personal services in an independent capacity shall be taxable only in that State, unless such services are performed in the other Contracting State and:
• (a)the individual is present in that other State for a period or periods aggregating more than 183 days in any consecutive twelve month period; or
• (b)the individual has a fixed base regularly available to him in that other State for the purpose of performing his activities, in which case so much of the income as is attributable to that fixed base may be taxed in such other State."
