Net migration, if you discount returning British citizens it currently sits at around 200,000 a year (500,000 gross), so it would be an approximate 20% reductio

Net migration, if you discount returning British citizens it currently sits at around 200,000 a year (500,000 gross), so it would be an approximate 20% reduction in non-British immigration. Or a 30% increase in emigration, but I doubt they're aiming for that.