A leading skateboard distributor has set up another business in the Netherlands to avoid paying tax twice on exports after Brexit.
Shiner's operations director said it would spend about £530,000 operating a base outside Rotterdam.
Some firms said current custom systems were "not fit for purpose", causing significant delays at the border.
The prime minister has said companies would be compensated for delays that were not their fault.
Richard Staite, of the company based in Almondsbury, South Gloucestershire, already pays 16% import duty on goods from China.
"If we then sell [items] on to one of our European customers we have to pay that import duty when we cross again into Europe", Mr Staite said.
He said the firm has opened its new European business and warehouse to avoid that "extra layer of bureaucracy" when operating on the continent.
"For the [UK] government there's a loss of corporation tax because all the profit is now profit that is being made in the Netherlands.
"We will be paying tax to the Netherlands rather to the UK government."
Andrew Varga, the managing director of Bristol-based Seetru Engineering, said the company has found it "impossible to generate new business within the EU".
The company makes high pressure valves, used by engineering firms throughout Europe.
But he said other firms were being put off from buying British by complex customs rules.
Mr Varga said: "It creates a bureaucracy that they do not have systems in place to manage.
"So however much they'd want to do it, the investment they would need to go into to build the systems to deal with us is just an absolute killer.
"The ones who export on have said they just cannot deal with us - as simple as that."
The Department for International Trade was approached to comment.