Half of British investors have seen their wealth decline since the UK voted to leave the EU back in 2016, compared with less than a fifth that have become richer.
That is according to findings from the Enterprise Investment Scheme Association (EISA), which estimates that there are 14.5 million less well-off investors since the Brexit vote.
It was also found that almost a third of investors believe securing a good deal with the EU is crucial for continued investment in smaller companies, yet nearly five in eight don't think the government is doing this.
The findings come after Brexit secretary Dominic Raab last week outlined how businesses up and down the country should prepare for a crisis departure from the EU.
EISA director general, Mark Brownridge, said: "The fact that so many investors feel this way is going to have a knock-on impact on the rest of the country and the economy.
"They feel that our government does not have their back, and in fact, is contributing to the negative sentiment surrounding Brexit."
The research involved a survey 1,122 nationally representative investors, finding that a third do not think there will be more opportunities for wealth creation and entrepreneurship post-Brexit.
However, an even larger amount believe there will be more opportunities, at 39%, with 10 million investors envisaging greater chances to invest in smaller firms, compared with seven million that don't.
The findings also show that a third of investors believe there will be a 'Brexit dividend' that will make the UK richer when it leaves the EU in March next year.
Some 43% of the respondents said that the government's actions affect their investment decisions more than ever before, compared with 14% that don't believe this to be the case.
"There is some positivity, with many feeling there will be great opportunities for wealth creation, entrepreneurship, and investment into SMEs in a post-Brexit Britain," Brownridge continued.
"We must remain optimistic yet cautious. We need to ensure investors have the confidence to continue to look to SMEs, and ensure there is enough capital for investors to reinvest back into UK businesses."