Though Britons are keeping a stiff upper lip about the future of bilateral U.S.-U.K. trade in the post-Brexit world, there are looming clouds of uncertainty for many American businesses that rely on transatlantic trade, one key voice in the British-American business scene acknowledged Monday.

Colin Brown, chairman of the British-American Business Council of Northern California, said that some companies in the Bay Area were shocked when the British voted last week to leave the European Union.

“We’re in uncharted territory,” Mr. Brown said. “It’s not quite clear yet what [leaving] means and the uncertainty is concerning. Some people view that as positive opportunity and some don’t like uncertainty. It’s complicated. It’s neither good nor bad — it’s uncertain.”

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Though he said a majority of the drama will unfold over the next two years of negotiations, the short-term question remains: What does the U.K. do now to attract business on its own, as opposed to part of a massive 28-nation bloc?

Mr. Brown said he feared that companies wanting to expand into Europe won’t use the U.K. as the bridge, opting instead to use other capitals like Madrid, Paris and Berlin within the EU as entry points into the continent’s markets.

The U.K. has seen some immediate results after the unexpected results came in on Friday as global equity markets were hit hard and the value of the pound dropped to historic lows.