Perhaps he thinks that he could be blackmailed because his daughter studying there. Do you live in England as a Pakistani national, or are you a British citizen? If you and your father are British citizens then you have to support England. And by the way it is the duty of every Muslim to be loyal to the country where he lives.
The claim/notion that the US government might blackmail Najam Sethi because his daughter is there is preposterous at best. This will be rejected by even the most avid conspiracy theorist that wander in the streets of our nation.
I disagree with Mr Sethi on most things. However, I have a lot of respect for the man. He has liberal/leftist stances because he genuinely believes in them and not because his daughter will be harmed by US government if he stops being a leftist.
I think Mr Sethi's observations are usually short sighted, he has no faith in the power Pakistan derives from the mass anti-Americanism, he preaches status-quo on some fundamental issues of governance and sometimes does not tell the complete truth when right wing, religious or conservative issues are at hand. On the other hand I admire his views on role of military, economy, military spending and ISI.
However, he is a patriotic Pakistani who believes what he preaches is for the good of the country. I disagree with him mostly but i reject the shallow claims of the highly sentimental, "emotions over facts" crowd that think everyone that disagrees with their vision of how things should be done to be a traitor, US/Israeli/Indian spy.