Myth 4: The UK's budget balance would improve substantially if we leave the EU.

A simple calculation suggests the UK would save £9 billion a year if it did not have to contribute to the EU’s budget (figure 1). Yet at least two-thirds of this saving would probably be eroded by the UK government compensating businesses and organisations that benefit from EU subsidies; continuing contributions into the European Economic Area (EEA) if the UK were to retain access to the single market; or losses from the positive contribution made by eurozone migrant workers.
Although we do not expect the UK economy to collapse if voters choose Brexit, the process of leaving would create uncertainty, which could reduce growth and, in turn, government tax receipts. As such, we do not believe the government’s fiscal position would change enough to cause a substantial reaction from gilt markets.
Source: OBR, datastream and Rathbones
The full whitepaper stating all related statistics and figures can be found here.