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Mystery Plane Spotted Again Circling London With No Callsign (It's Also On YouTube)

23/07/2014 12:22 BST | Updated 23/07/2014 16:59 BST

Another mysterious plane has been spotted circling above London with no callsign -- and the Mayor's office will not say why.

The mystery began on Tuesday, when HuffPost spotted a plane with no callsign and the registration number G-BVJT circling for hours above South London.

It was clear from the outset that we were not the first to spot the plane, or to remark on its unusual flight pattern. The planes have been found numerous times on plane-spotters' forums and social media, and not just above London.

After another brief search above London's skies on Wednesday morning, another plane of exactly the same type (a Cessna F406 Caravan II) and with a similar flight pattern was obvious in the skies -- though it had a different registration number - G-TDSA - and was circling in a different area closer to Central and North London:

flightradar24

Here's another picture:

flightradar

It is still unclear who operates the plane, but it is thought to be part of an an official covert surveillance program.

The Telegraph reported in 2011 on a similar - though not necessarily the same - program operated by the Metropolitan Police since 1997, at a cost of around £3 million annually, possibly connected to the monitoring of mobile phones.

And now it has emerged that leader of the Liberal Democrat Assembly group, and Chair of the London Assembly's Transport Committee, has directly asked Mayor of London about the planes -- and received a blunt answer.

On June 11 Caroline Pidgeon asked at Mayor's Question time:

"Can you tell us who is in charge of the deployment of the MPS's two Cessna aircraft and what is their remit?"

The Mayor's office replied:

"For operational security reasons, it is not appropriate for MOPAC to respond."

She also asked:

"How much was the capital cost of the MPS's two Cessna aircraft, registrations: G-TDSA and G-BVJT? What is their annual running cost?"

And received the same answer.

Pidgeon told HuffPost that the Mayor should be open about the planes' existence, and how much they cost:

"Of course the Met needs to defend some secrecy over its surveillance work, however you can’t put planes up over London without people noticing. It would be best if the Met simply admitted that vital surveillance work takes place and at the same time was open about the costs of such operations."

The only official documentation online about the two planes indicates they are privately owned, and operated by a series of companies about which little external information is available.

However, the planes have also made another appearance in recent months -- on YouTube.

Footage of what appears to be a Cessna F406 with the registration G-TDSA printed on the wings can be seen on the video site, allegedly taking off from near Cambridge. We have no way to independently confirm if this is the same plane as spotted on FlightRadar 24, or if the details in the description are accurate.