MI5 has issued an unprecedented warning that China is attempting to corrupt Britain's military staff to steal secrets.

Together with Britain's domestic intelligence agency partners in the 'Five Eyes', it released a bulletin titled 'Safeguarding our Secrets'.

The document called out China's military intelligence services after a surge in espionage bids to entrap the armed forces.

The warning comes just days after Foreign Secretary Yvette Cooper travelled to Beijing this week for security talks in which she spoke of Britain and China's 'shared interest' in a rules-based international order.

It is the first time the Five Eyes partnership between the UK, US, Canada, Australia and New Zealand have jointly issued any bulletin about hostile state activity.

The decision to send a united message comes after spies have seen a sustained espionage campaign from China's military intelligence services. The bulletin warns Beijing's spies are 'attempting to recruit and cultivate long-term relationships' in exchange for 'classified or privileged information'.

In a new escalation Chinese teams are pursuing an 'aggressive online recruitment strategy' to woo military staff, posing as employees of private consultancies, think tanks and human resources firms.

MI5 has identified scores of bogus job adverts for foreign policy and defence analysts on professional networking sites and online platforms offering big salaries to trick military staff into divulging secret information. 

The advisory warns: 'China's military intelligence services ultimately seek to acquire privileged military, political and economic intelligence that can provide China with a strategic and tactical advantage over the Five Eyes.'

Those being targeted include military personnel, particularly those stationed in the Indo-Pacific region. Another priority is entrapping anyone with 'security clearance', but anyone with access to government information including academics, journalists or think tank employees, is also at risk.

In 2023, MI5 chief Sir Ken McCallum warned Chinese spies had targeted more than 20,000 British officials on LinkedIn. 

But tactics have evolved with bogus recruitment companies or spoofed legitimate firms offering 'too good to be true' opportunities. In some cases, British professionals are being offered up to £2,000 for a single report on defence.

While the initial contact may be on a professional job platform, it will quickly move to communications on an encrypted platform. 

Resumes for the phoney jobs are 'ranked based on likelihood of access to sensitive information'. The practice usually involves payment via unconventional means such as cryptocurrency, or from accounts that do not share the firm's name.

Victims can then be enticed into flying to a non-Western country and pressed into spying for Beijing.

Security Minister Dan Jarvis said: 'We have taken robust action to defend our country and will continue to tackle hostile actions from a range of states including China.'