The benefits of a double taxation agreement are only available to persons who are a resident of one (or both) of the contracting states (art. 1 of OECD Model: see Schwarz on Tax Treaties¶14-100).
The vast majority of the UK’s double taxation agreements follow closely the OECD Model in defining a ‘resident of a Contracting State’ as any person who is liable to tax in that state by virtue of some connection with it in the form of either residence, domicile, place of business or similar test. It is not sufficient that a person’s income may arise in that state (art. 4(1) of OECD Model).