@Oilyvoir
Could it be that they want to do a comparison of infection rates with schools open and closed? The boroughs that are still open seem to be a cross section of London boroughs in terms of geography. In our household of 3 - 2 teachers and a Y1 child - we cover 3 different closed west London boroughs, 2 of which border Harrow. Northwick Park hospital which is the local one for Harrow was overrun with covid last time. Not sure how they are doing now. It will be interesting to see how Harrow does in comparison to our boroughs over the next couple of weeks. Interesting but a dangerous game on the governments part.
If so, it's an incredibly flawed experiment. As you say, you're in 3 different boroughs. At our school, we have many families who have children in schools in 2 boroughs, and some in 3 boroughs. Most staff do not live in our borough, and about 1/3 of our pupils don't either. So case rates per borough will continue to be borderline meaningless.
I know you're not advocating for this, merely speculating. I think it's appalling that we've not been told and therefore only have speculation to go on.