Durhamjen
The mentioned 2% increase in GDP if offset by the cost of residency in the UK would probably show a negative benefit. The additional housing, education, health, social benefits and other services,plus the need to import food and goods adding to more waste and sewage must be factored in.
If all of the immigrants were within the high income brackets these costs would eventually be mitigated through income tax payments, however a vast majority are in the mid to low income brackets where there is often little or no tax paid and high benefit received. Ideally immigrants should have an overall positive impact both to the economy and to the workplace with specialist skills that are not met by the indigenous population.