CHINESE officers who attended an RAF training course in a goodwill exchange programme spent 60 per cent of their free time spying on a top secret North Yorkshire military base, it has been claimed.

Lt G Huang and Capt S Tong are alleged to have repeatedly made the two-hour, 130-mile journey from Royal Air Force College in Cranwell, Lincolnshire, to RAF Fylingdales, on the North York Moors.

The radar base at Snod Hil, near Whitby, provides a ballistic missile early warning and space surveillance service to the UK and US governments.

Such is the sensitivity of the work at RAF Fylingdales, which is based on 3,000 acres of moorland, that it is guarded by 80 military policemen.

It has been reported that a classified dossier on the off-duty actions of the Chinese officers, who claimed to be ground engineers, has been presented to Theresa May at the insistence of US Intelligence chiefs.

The Prime Minister is believed to have considered the document alongside MI5 reports about Chinese commercial espionage, before putting plans to build Britain’s first nuclear power station in decades at Hinkley Point on hold.

It is understood the Chinese officers may have been interested in the upgraded early warning radar system at the base, which is expected to receive formal certification of capability to support the fourth mission of US Missile Defense in the near future.

The officers were the first Chinese airmen to be trained at the Royal Air Force College in Cranwell, Lincolnshire, as part of an initiative which aimed to improve relations with the China.

They were also given weekend passes to leave RAF Cranwell and graduated last October, with Air Vice-Marshal David Stubbs presenting their wings, after an 18-month course. The pair are now said to be working at a ballistic missile installation in northern China.

The Sunday Express reported a British intelligence source as stating: “It was decided early in their stay that their out-of-college activities would be closely monitored.

“At times they would go straight here. At other times they would visit another location on the way.

“The report makes it very clear these two individuals were high-level intelligence officers, and not just the ground engineers they purported to be.”

Intelligence officers are said to have estimated the Chinese officers spent more than 60 per cent of their free time observing the site and particularly its active electronically scanned radar array.

The Ministry of Defence declined to comment.