It's interesting to note that the Remain campaign mostly use words like MAY and COULD in their scaremongering tactics. This of course means they have no idea. Brexit, however, can say that - in broad terms - the working-age native population is in fiscal credit while the equivalent immigrant population is in fiscal deficit. We also know that, "... the total expenditures on immigrants exceeds revenues by £16.8 bn. On this basis it is hard to see much support for the contention that immigrants - or even recent immigrants - as an undifferentiated group are helping to reduce the fiscal burden for native workers or contributing to reducing the UK's fiscal deficit." Taken from a recent report by Migration Watch,
http://www.migrationwatchuk.org/briefing-paper/381.