While British military personnel frequently take part in training exercises with foreign armies, any work by pilots with China - which London has dubbed the "No 1 threat" to its security - is a serious concern in the UK.

"We are taking decisive steps to stop Chinese recruitment schemes attempting to headhunt serving and former UK armed forces pilots to train People's Liberation Army personnel," a defense spokesperson said.

Armed forces minister James Heappey acknowledged to broadcaster Sky News that such collaboration "has been a concern within the Ministry of Defense for years."

He added: "Our counter-intelligence people have been looking at it closely. The recruitment of pilots in order to understand the capabilities of our air force is clearly a concern to us and the intelligence part of the ministry.

"China is a competitor that is threatening the UK interest in many places around the world. It's also an important trading partner.

"But there is no secret in their attempt to gain access to our secrets and the recruitment of pilots in order to understand the capabilities of our air force is clearly a concern to us."

Heappey also said officials have been warning pilots involved to quit.

"We are going to put into law that once people have been given that warning it would become an offense to continue with that training," he said.

More than 30 former pilots are said to have accepted offers upward of 240,000 (HK$2.12 million), with many of those recruited in their 50s and having recently left the British Royal Air Force.

The practice has supposedly been going on since 2019 but has been stepped up recently.

A ministry spokesperson said officials were now "reviewing the use of confidentiality contracts and non-disclosure agreements."

All serving and former personnel are subject to the Official Secrets Act that prohibits UK public servants from sharing state secrets with foreign powers, the spokesperson added.

"The new national security bill will create additional tools to tackle contemporary security challenges - including this one," the spokesperson said.

In Beijing, however, Foreign Ministry spokesman Wang Wenbin denied knowledge of any such employment of British pilots.

Relations between London and Beijing have soured following China's crackdown in Hong Kong and disputes over technology giant Huawei's involvement in the roll-out of Britain's 5G network as well as concerns about human rights and influence peddling.

In a speech in London this month, the director of Britain's GCHQ spy agency, Jeremy Fleming, warned that China's growing technological dominance was "an increasingly urgent problem" for Western countries, urging them to defend their values and influence.