Business investment was running about 5% lower than could be expected in the first half of 2016 but will pick up in the event of a Remain win, with 70% of delayed projects expected to go ahead later this year.
The CEBR said not all the investment shortfall would disappear if the country votes to Leave – around a third would go ahead over the next 12 months – and a falling pound could make the UK more competitive in export markets.
CEBR president Douglas McWilliams said: “We shouldn’t be surprised if there is an economic bounce back after the referendum, whatever the result.”
But the think tank warned there is likely to be a “slump” in manufacturing investment.
Mr McWilliams said: ” The Brexit referendum has had an effect on the real economy. At one level it has triggered substantial spending on advertising, propaganda and events. At another level it has driven gyrations in the financial markets which have broadly tracked the changing probabilities of a vote to remain in the EU.
“There has also clearly been a delaying of investment projects, both from inward investors and from indigenous investors.
“To try to understand the scale of the likely post-referendum mini-boom, we have investigated the scale of the investment shortfall carefully and attempted to analyse how much of this investment might bounce back during the rest of the year after the vote.
“Looking at the total of business investment, we estimate that this has been running for the first half of 2016 about 5% lower than can be explained using our economic models and assume that this represents the scale of the business investment shortfall. There was also a much smaller shortfall in Q4 2015.
“In total this amounts to a shortfall of investment of £5.9 billion at current prices.”
This included around £3 billion in IT investment, £1 billion in building investment and around £2 billion in plant and equipment.
The CEBR said it believed a Remain win was “highly likely” and with 70% of the delayed projects forecast to go ahead in 2016 ” business investment, particularly in IT, could be booming” the second half of the year.
If the country backs Brexit ” much of the service sector will be subject to no change in trading conditions whether the UK is in the EU or outside, though for the manufacturing sector the situation will be different”.
“We believe that even if the UK votes leave about a third of the investment backlog will be activated in the coming 12 months, though there is also likely to be a manufacturing investment slump,” he said.