Productivity is a key driver of our data used in this calculation – particularly productivity in the tradable goods sectors. This is likely to suffer after Brexit due to non-tariff barriers to trade (think complying with overseas regulation and customs regimes). That said productivity growth in Europe has been weak, and is unlikely to surge ahead while the UK economy recalibrates, somewhat limiting the damage to the equilibrium rate. If the European project revives around a new Macron/Merkel nexus, then further gains from integration may lower the equilibrium rate a little further via improving Eurozone productivity.
Although the long-run economic value of the pound would shift lower in a ‘hard Brexit’ scenario (i.e. no special deal), primarily due to the impact on productivity, the actual exchange rate is so far below the economic equilibrium value that we expect the pound to rise on a long-term basis in any scenario. It is really just a question of speed.
Unfortunately, such long-term analysis does not help us forecast currencies on a 6-12 month view, and the newspaper headlines generated by ongoing Brexit negotiations could well drive exchange rate volatility.
Until June, the EUR/GBP exchange rate over the last couple of years has closely tracked changes in relative interest rate expectations (i.e. what the market thinks interest rates will be in Europe in 3 years’ time relative to what they think they will be in the UK). This lends some shorter-term support to the pound, and indeed could favour sterling further if the run of strong data in the Eurozone starts to decline.