The 'mystery plane' caught at regular intervals circling London for hours for no apparent reason, might have been caught on film.
The planes, which regularly appear on FlightRadar24 and similar apps 'without callsigns', have been seen in flying very mysterious routes over the capital all week.
The police have since "refused to deny" that the planes are in fact used for spy operations over London and other towns. London mayor Boris Johnson has also refused to answer questions on the planes for "operational security reasons".
Now footage has emerged on YouTube, uploaded earlier this year, that appears to capture the same type of plane as has been jotted down by plane spotters.
The plane is a Cessna F406 Caravan II, a 12-14 person capacity plane with 2 turboprob engines.
It appears to have the same registration number on the underside of its wings as the plane seen over London earlier on Wednesday, and the video claims to show it taking off from near Cambridge. The video also shows that the plane has its rear windows blanked out, possibly indicating (as expected) that there is more inside the plane than empty seats.
It remains impossible to tell exactly what the planes are up to, but it is thought surveillance of mobile phones might be involved.
Earlier Liberal Democrat London Assembly member Caroline Pidgeon told HuffPost:
"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."