The boss of crowd-funding giant Seedrs has likened Conservative plans to curb skilled migration to "shooting ourselves in the head" and warned over the threat of Brexit to the technology sector.
Jeff Lynn told the Press Association that Theresa May's proposal to double the immigration skills charge to £2,000 a year for every skilled non-EU migrant a company employs is "baffling".
"Is Brexit about making us a more open and global country? Having talented people from around the world come to this country is only a good thing, and the notion that we would do anything to make that more difficult is just shooting ourselves in the head.
"I'm baffled by the idea that we are looking to increase the skills tax," he said.
The American chief executive also railed against Brexit, saying it is "not good for Britain" and that investment in the tech sector will diminish as a result of Britain's decision to quit the EU.
Like several other financial firms Seedrs, which acts as a marketplace for early stage investment in companies, is also weighing up plans for an EU hub.
"We do have a financial services passport and might have to look at getting some sort of dual authorisation in Dublin or something like that.
"If you have a serious economic slowdown or, as a result of trying to stop skilled migrants coming in, a reduction in the number of entrepreneurial businesses, then it will be an issue.
"If talented young entrepreneurs who would have once come to London to start a business are now going to do so in Berlin, we will do more deals in Berlin.
"If we start finding that the talent is located elsewhere, that'll probably cause a talent shift for us."
However, Mr Lynn said any movement in staff numbers from London, where the firm employs 40 people, will be reasonably small.
Seedrs is also looking to launch in the US later this year as the firm embarks on ambitious growth plans.
The firm is currently providing a platform for 10 to 15 deals a month and has seen about £220 million invested since launching in 2012, but Mr Lynn wants to take a much bigger chunk of the market.
He said: "We're still a drop on the ocean compared to where we want to get to.
"The market we're going after is probably worth £30 billion to £50 billion a year. At scale, we feel we could be doing up to £1 billion of that."
As part of the push, Seedrs is working on a number of new innovations to appeal to a wider group of investors, including the launch of a secondary market.
Behind some of Seedrs' success has been the falling appeal of investing in public markets, Mr Lynn added.
"The appeal of the public markets as a place to earn returns has gone down. Companies are going public later, once all of the exciting growth has already happened," he said.