According to Treasury and OBR numbers higher rates of inward migration boost growth and can lower the deficit . It is of course right that if you add in a lot of new low paid migrants GDP goes up. It is also true GDP per head goes down with the encouragement of more low paid employment.
The OBR we read is minded to increase their forecast of the deficit if we have fewer migrants. This is odd. Low paid and no paid migrants need subsidised housing. They need a range of free and subsidised public services. They add to the need to build new roads, surgeries, schools, hospitals, power generation and sewers. Much of this has a direct public spending cost.
The OBR may need to revise its assumption about productivity growth down for other reasons. Public sector productivity is still well below 2019 levels and the public sector is out recruiting. Private sector productivity has the huge headwind of accelerated energy and industrial closures. Oil, gas, petrochemicals and the manufacture of petrol cars all deliver high labour productivity. All are being run down by bans, high energy prices and regulations. Current OBR forecasts say productivity will recover to 2% a year by the end of this decade, and average 1.25%