"People can allege that Jemima Khan is shagging Jeremy Clarkson and say that the press isn’t reporting this because of a superinjunction. ... In this way, Ms Khan’s reputation is damaged by the existence of super injunctions (though the social cost of this is mitigated by the fact that Mr Clarkson‘s reputation is enhanced)."
Ms Khan attracted a lot of publicity to herself when she chose to protest about various allegations about her and Mr Clarkson that had been circulated on Twitter. Most people looked at the allegations and dismissed them as highly unlikely. The story, repeated with glamorous pictures in all newspapers, has merely served to remind us about her wealth and beauty, and has probably only enhanced her reputation. Perhaps the real purpose of her protest was to deflect attention and credibility from some other allegations. (See my post on Google-spinning.)
Chris assumes that Ms Khan's reputation would be sullied if she were discovered to have had a relationship with anyone outside the usual round of actors and sportsmen and other good looking airheads. Although I'm not a fan of Mr Clarkson, I imagine that a wealthy and bored woman might find a discreet relationship with him to be quite interesting, and I can't see that her reputation would be particularly damaged. It's not as if she were caught attending one of Mr Berlusconi's or Mr Mosley's parties, or spilling out of nightclubs in a dishevelled state.
Meanwhile, Chris assumes that Mr Clarkson's reputation is enhanced by these allegations. Again, I can't see that a popular and happily married journalist wants to be associated with bored heiresses, let alone by their indignant denials.