  We perform stochastic microsimulations of the dynamics of England and Wales
population after the British referendum on EU membership, considering different
possible outcomes. Employing available survey data, we model the demographics
of the region over the next generation, as shaped by births, deaths and
international migration. The migration patterns between England and Wales and
the remaining EU countries are modified according to the possible scenarios of
their future relations. We find that Brexit will accelerate the overall
population ageing and the deepening imbalance between workers and retirees but
reduce the population growth and the fraction of women of reproductive age. In
the alternative scenarios of remaining in the EU these effects will be
partially forestalled by the influx of immigrants from current and prospective
EU countries and their children. In all considered scenarios the native British
population declines. Our study demonstrates that microsimulations can be a
useful tool for designing and evaluating the country's policies in the advent
of fundamental transformations.
