Alphabet  (GOOGL) and Apple's (AAPL)   recent London investments mask a deeper concern for the city's future as a global tech hub as the government grapples with Brexit and rivals in Europe and Asia attempt to lure talent.

Google's plans to build a new London HQ in the city's King's Cross district and add 3,000 new jobs has been seized by the British government as a validation for its post-Brexit future. The move follows Apple's decision to shift 1,400 of its staff to London's Battersea Power Station, best-known as the photographic backdrop to the famous Pink Floyd album "Animals". Amazon (AMZN) also appears committed to its new east London office in Shoreditch in an area known as 'Silicon Roundabout'.

But in a fast-paced technology industry where speed matters, some say Brexit confusion -  a leaked memo Tuesday accused the government of having "no overall strategy" for leaving the EU - has complicated re-location and investment plans.

A survey conducted by London's Magister Advisors showed that a non-U.K. software company placed 100 engineers in Germany rather than Britain immediately following the June 23 referendum and a fintech company decided in August to shift dozens of jobs to Dublin. 

"I reckon people will be making decisions during next year," said Magister's MD Victor Basta. "These companies are growing 50% a year. You can't tolerate three years of uncertainty. If there is a degree of uncertainty by late next year, it will force a bunch of people to make decisions they otherwise didn't have to make."

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