This is actually a swing to Goldsmith compared to Johnson last time and is closer than London as a whole (which is not... normal). The concern is that possibly the whole mini Modi business worked, and I dread to think what the future implications of that might be. Though we'll need to look over ward figures (when they're out).
Of course I could wikipedia it and find absolutely nothing on the demographics but notice that the depleted LibDem and Green vote tallies and the Respect score of 3% explain most of the shift you mentioned, but I would still be in the dark as to what's going on there, plus it's always such a pleasure to hear of these things with your words, Shibboleth! 
Both boroughs have large Hindu communities (25% of people in Harrow and 18% in Brent) and Zac Goldsmith's campaign produced campaign literature which implied support for Indian Prime Minister Narendra Modi, who is a Hindu nationalist.
