Do you mean "BBC World News"? I don't think just "BBC World" is a channel.
I get BBC World News on channel 167 (SD only, apparently). It appears that you need a tier with at least 220 channels, like Preferred Pro or Premier Pro.
I think why I might get BBC world news in HD is because I have x1box and xfinity internet I know all new channels that have been converted to HD over the last year and a half have come over IP but you may or may not have to have internet to get new channels converted to HD maybe someone can confirm on this forum
I think it is among the standard news channels like CNN ect.. I have it on my X1 box line up, in HD. Perhaps your area doesn't have the capacity for all the HD offerings xfinity has...