NRI opening business in India

A citizen of UK (Indian origin) wants to open his business in India. He will be providing consultancy and advisory to the clients who want
to visit UK. What will be the taxability of his income from his office in India, if he is non resident of India according to the Income tax Act?
He is having income from his business in UK as well. What tax relief he will get if he is resident or not ordinarily resident? Will the DTAA
between India and UK comes to his benefit?