It predicts the influx will provide a boost in tax receipts and a fillip for potential output growth.
The government initially promised to cut net migration – the sum of those entering the country less those leaving – to 100,000 by the end of the election, but the OBR has now raised its projections by 57 per cent to 165,000, a huge jump from the previous prediction of 105,000.
What's more, the figures are expected to drop to that number by 2019, and may be higher during the intervening years. Net migration rose to 298,000 for the year to September 2014, up from 210,000 for the same period a year earlier.
The OBR report said:
Our previous forecasts have been underpinned by the assumption in the ONS low migration population projections that net migration will move towards 105,000 a year by mid-2019. A reduction over time seems consistent with the international environment and with the Government’s declared efforts to reduce it.
But in light of recent evidence, it no longer seems central to assume it will decline so steeply. So we now assume that net migration flows will tend towards 165,000 in the long term, consistent with the ONS principal population projections.
The report also says that a fall in government tax receipts from lower-than-expected North Sea Oil revenues and a drop in Stamp Duty due to falling home sales would be partly offset by a rise in tax receipts driven by higher than predicted immigration.