IS there something we should know? What appears to be a spy plane has been spotted circling the city, but its purpose is a mystery.

The plane, which looks to be a Sentinel twin-jet aircraft, was seen in the clear blue sky above Worcester yesterday.

It was well above 2,000ft, the level below which all traffic is monitored by RAF air traffic controllers who were unable to shed any light on its identity.

And despite the Worcester News putting in calls to civilian air traffic controllers, the plane’s purpose remains a complete mystery.

It is not the first time an unidentified aircraft has been spotted gracefully circling the Faithful City, but it is the first time this type of plane has been spotted.

The aircraft, which was photographed by @wildaboutimages on Twitter, appears to show a Global Express-type fuselage, which is built by Canadian firm Bombardier.

The military version – the Raytheon Sentinel – has a distinct ‘bulge’ under the front of the cockpit, which can be seen on the photo, and the RAF operates a compliment of the planes from RAF Waddington.

But an RAF spokesman said Waddington had no planes out over the area yesterday between the times it was sighted, from 9am until 2pm. Twitter user Sean Mooney appeared to contradict that, however, when he said: "I can confirm it was the Sentinel of 5 Sqn Waddington as I work on it."

The Ministry of Defence has announced its RAF Sentinel planes, adapted to carry sophisticated radar, are being pulled from service to save money on the defence budget once Britain completes its withdrawal from Afghanistan.

Air traffic controllers at Birmingham Airport, who guide civilian passenger planes passing over the city’s airspace, said they had not registered any planes under their control circling the city.

Meanwhile, a spokesman for the NATS, which provides air traffic control across UK airspace, said they had had “no issues” with civilian aircraft yesterday, suggesting the aircraft was likely military.

One possible explanation is it could be a United States Air Force plane operating from RAF Mildenhall in Suffolk.

The circling aircraft, which left wide oval-shaped contrails over the city and neighbouring counties, sparked much interest on our Facebook page here, with many of our fans speculating as to its purpose.