One of the three men is the husband of an MP from the governing Labour Party.
The three allegedly assisted a foreign intelligence service in violation of the National Security Act of 2023, Metropolitan Police said.
Police did not name the suspects because they have not been charged.
They said one was a 39-year arrested in London, another was a 68-year-old arrested in Powys, Wales and the third, a 43-year-old, was arrested in Pontyclun, Wales.
With calls growing for one of the three to be named in light of speculation that he was the husband of MP Joani Reid, the member of parliament for the Scottish constituency of East Kilbride and Strathaven, she issued a statement indicating that her husband was among those arrested while insisting that she herself was not involved.
She did not name her husband David Taylor, who is 39.
"I have never seen anything to make me suspect my husband has broken any law," she said.
"I am not part of my husband's business activities and neither I nor my children are part of this investigation, and we should not be treated by media organisations as though we are."
The arrests are the latest in a number of arrests in the United Kingdom of people accused of spying or causing political interference on behalf of China.
The domestic intelligence agency MI5 issued an alert to MPs in November warning that Chinese agents were making "targeted and widespread" efforts to recruit and cultivate them using LinkedIn or cover companies.
Chinese authorities have strongly denied those claims, calling them a fabrication and malicious slander.
UK officials complained to their Chinese counterparts about the latest arrests, security minister Dan Jarvis said.
"The government has been consistent and unambiguous in our assessment that China presents a series of threats to the United Kingdom," Jarvis said.
"We remain deeply concerned by an increasing pattern of covert activity from Chinese state-linked actors targeting UK democracy."
Police do not believe there was an imminent or direct threat to the public related to the arrests, head of counter terrorism policing in London Helen Flanagan said.
"We have seen a significant increase in our casework relating to national security in recent years and we continue to work extremely closely with our partners to help keep the country safe and take action to disrupt malign activity where we suspect it," Flanagan said.
with PA
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