LONDON— Britain's top domestic spymaster cautioned the population on Wednesday to treat the threat of spying from Russia and China as vigilantly as terrorism, warning that foreign spies were seeking to steal technology, sow discord and attack infrastructure.

The 9/11 attacks on the United States almost 20 years ago made tackling terrorism the biggest priority for Western intelligence agencies, with vast resources focused on the threat from home-grown and foreign-based militants.

But the growing assertiveness of post-Soviet Russia and the rise of China has forced the West's most powerful spymasters to return their focus to old-fashioned counter intelligence, or spies tackling other spies in a constant cat-and-mouse game.

Security Service (MI5) Director General Ken McCallum said that British intelligence had clocked 10,000 disguised approaches by foreign spies seeking to manipulate ordinary people in Britain.

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The consequences of spying by foreign powers can range "from frustration and inconvenience, through loss of livelihood, potentially up to loss of life," McCallum will say in a speech at Thames House, MI5's London headquarters.

"We must, over time, build the same public awareness and resilience to state threats that we have done over the years on terrorism," he said in excerpts of his speech released by MI5.

"You don’t have to be scared; but be switched on."

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British spies say China and Russia have each sought to steal commercially sensitive data and intellectual property as well as to interfere in politics and sow misinformation.

Beijing and Moscow say the West is gripped with a paranoia about plots. Both Russia and Chine deny they meddle abroad, seek to steal technology, carry out cyberattacks or sow discord.

McCallum, a career spy, said the whole country should be alert to the threat of foreign spying.

"We see the UK’s brilliant universities and researchers having their discoveries stolen or copied; we see businesses hollowed out by the loss of advantage they’ve worked painstakingly to build," he said.

"Given half a chance, hostile actors will short-circuit years of patient British research or investment. This is happening at scale. And it affects us all. UK jobs, UK public services, UK futures."

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MI5 began as a counter-intelligence service in 1909, first focusing on the threat from Germany and then, after World War 2, focusing on the Cold War threat posed by the Soviet Union's agents.

McCallum will also speak about the dangers emanating from Northern Ireland, far right groups and the withdrawal of forces from Afghanistan.