MI6 is expected to grow from 2,500 to nearly 3,500 to provide extra security for their operations and staff, according to BBC sources.
Alex Younger, who made a rare public appearance at a security conference in the US this week, warned that the internet andtechnological advances presented both an "existential threat and a golden opportunity".
"The information revolution fundamentally changes our operating environment. In five years' time there will be two sorts of intelligence services - those that understand this fact and have prospered, and those that don't and haven't. And I'm determined that MI6 will be in the former category," Younger said.
The boost to MI6's staff numbers is part of a wider commitment by the UK government's 2015 'Strategic Defence and Security Review' to recruit 1,900 extra personnel to the intelligence services.
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The remaining 900 new personnel will be split between the other UK spy agencies - Security Service (MI5) andGovernment Communications Headquarters (GCHQ).
Younger appeared at the security conference in Washington DC earlier this week alongside CIA director John Brennan and their Australian and Afghan counterparts.
"I would like to be optimistic about this but we have got quite long experience of this phenomena now and I see it very much as the flip side to some very deep-seated global trends, not least of all globalisation, the reduction of barriers between us," he said.
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