Building on the green belt crucial to solving London's housing crisis

The mayor's move to protect London as a place for work is welcome, but tough decisions on housing need to be made

In a city with demand for housing as high as London, it might seem odd for the mayor to intervene to stop office space and commercial properties being redeveloped as new homes.

Yet that's exactly what Boris Johnson did last week, by publishing new guidance aimed at preserving the capital's "central activities zone", which runs from Paddington to Aldgate, for retail, office, cultural and business use, and to ensure that these areas don't get lost to new housing.