The IFS clearly missed fhe referendum debates. Leave won, making it clear we wish to leave the EU and have no wish to go on paying contributions or accepting freedom of movement.
There is no evidence that joining the EEC or completing the single market boosted our growth, so it is difficult to believe we will lose growth when we leave.
The IFS agreed with Remain. The official campaign made plenty of false claims and stupid forecasts about what would happen if we voted for Out. Why don’t they accept they got it wrong and start looking at the facts for a change?