Yet more vicious nonsense. Here is the interview where Sadiq Khan used the phrase "uncle Toms".
I'm not sure exactly what he meant by using the phrase as it's not terribly clear. I guess he may have been trying to say that it's no use just talking to people who agree with you. Who could disagree with that? Whatever he meant by using the term, I think it's pretty clear he meant nothing like the implication that's been made: that somehow he opposes moderate Islam. That's just patent nonsense.