it's prolly what he *didn't* do that earned this epithet.
@jgilbert there was a famous bit of graffiti in North London on a bridge over a major road that said “M Khan is bent”. It was made famous by a TV Show called the Mary Whitehouse Experience who claimed that it had been seen by 2,956,500,000 people (300,000 cars per year with 2.7 people - assuming that no one person drives past twice … so, highly questionable maths).
I’ve heard two explanations over the years, both of which are much darker than the TV show and which align with two of the multiple different meanings of the word “bent” in British English - “corrupt” and “gay”.
The first that Khan was a corrupt policeman who had put someone away unjustly and this was the family’s protest.
The second was a court case where a 15 year old boy had killed a middle aged man with a pan when he had sexually assaulted him.
I can’t verify either explanation.