Maybe it's splitting hairs, but I think it depends what pairs you compare to arrive at the conclusion that they sound the same (= are homophones) or that they don’t, respectively.
Of course the BE pronunciation is different from the AE one, hence the different IPA representations. So if you compare BE to AE, they are not homophones.
But if you gave a BE speaker a piece of paper with "knew" and "new" written on it and had him or her pronounce both words, they would sound the same (/nju[FONT="]ɪ[/FONT]/), i.e. they would be homophones.
The same goes for an AE speaker. Both words would sound the same (/nu:/).
Or am I getting something wrong here? :-?