Vodafone, the telecoms giant and one of Britain's biggest tech firms, may move its headquarters out of the UK following the country's vote to leave the EU.
The company, which employs 13,000 people in the UK, said it can't commit to keeping its HQ in London until it has a better understanding of Britain's future relationship with the EU.
"The UK's membership of the European Union has been an important factor in the growth of a company such as Vodafone," a company spokeswoman said.
"It remains unclear at this point how many of those positive attributes will remain in place once the process of the UK's exit from the European Union has been completed. It is therefore not yet possible to draw any firm conclusions regarding the long-term location for the headquarters of the group."
Across the Vodafone group, she said the "very large majority" of the firm's 462 million customers, 108,000 employees, and 15,000 suppliers are based outside the UK.
More than half (55 percent) of Vodafone's group earnings before interest, taxes, depreciation, and amortization (EBITDA) are generated by its mainland European business, compared to just over one tenth from inside the UK.
Pan-European businesses such as Vodafone rely on freedom of movement of people, capital, and goods throughout the region, she said. At this moment in time it remains unclear whether a future UK government would be willing or able to forge a trade deal that would guarantee these freedoms.
However she added that Vodafone would "continue to invest in our UK local operating company in future".
Job creation will also be hit among smaller tech firms. The data analytics startup DueDil will scale back plans to create new posts inside the UK.
The London-based firm, which employs 100 people, said it will focus on growing the business inside Europe.
"There's no doubt that we'll be slowing plans in the UK and accelerating them abroad," a spokesman said.
"We'll take decisions as part of a structured plan to expand into Europe and become an international company, based in the UK."
A survey by the UK's Institute of Directors at the weekend revealed the majority of members felt that Brexit would affect them negatively. One in four said they were putting hiring plans on hold and 5 percent intended to make staff redundant.
There was better news regarding the Chinese technology giant Huawei. Yesterday UK business minister Sajid Javid told a news conference that the firm's planned £1.3 billion investment in the UK would go ahead as planned.