Those responsible for planning London’s future naturally look to experts to tell them how the capital’s population will change. But this graph, which tracks London’s mid-year population estimates from 1967 to 2015, shows that most official projections have been wide of the mark. Early predictions underestimated the decline; more recent ones underestimated the rise.

The models used by London’s demographers have become increasingly complex – these days they tend to offer a range of projections based on different assumptions, rather than a single forecast. A recent set of projections from the Greater London Authority in 2012 demonstrates this. For one projection, they used a trend-based model (J), resulting in a higher population trajectory than another based on housing and household formation data (I). The increasing complexity of models should lead to more accurate projections, although it seems likely there will always be unknowns.

What does the future hold? Some early indicators suggest Brexit is suppressing immigration to London, which could reduce population growth – although this may be offset by increased migration from within the UK. If past experience teaches us anything, however, it’s that population projections are extremely unreliable.

Source: Actual population from GLA (2016). Projections from indicated documents, assuming linear change between contemporary and projected population where necessary. Based on data provided by Tony Travers, Director of LSE London.