You asked
I would like to formally request the area size (in kilometres squared) of all the boroughs within London. If you have released this already that would also do nicely.
We said
The requested information is not held by the Office for National Statistics.
The list can be downloaded from https://www.lgbce.org.uk/records-and-resources/local-authorities-in-england
You may also find this information to be of interest http://data.london.gov.uk/dataset/land-area-and-population-density-ward-and-borough