Police are coming under mounting pressure to reveal details of a mysterious spyplane said to eavesdrop on mobile phone calls.
A radar tracking website showed an aircraft circling London at 10,000 feet for more than two hours yesterday.
The plane had no recognisable callsign but was identified as a twin-engine Cessna F406 with the registration G-BVJT.
The aircraft has also been operating in other parts of the UK. Its movements over Leicester were captured by a flight tracking website in May.
The aircraft has been linked in the past to shadowy fleet of surveillance planes said to be operated by the Metropolitan Police.
Darren Burn, who lives beneath the flight path says he also saw a second spyplane.
About 6.30 last night I could hear and see a light aircraft circling for over an hour around my house in Oval. I downloaded a flight tracker and discovered that it was another unmarked aircraft similar to what I'd read about earlier in the day. It had a tail sign G-UMMI. >
Reports suggest the two planes, costing £3m a year, are used to monitor mobile phone calls.
The Liberal Democrats have called on Boris Johnson as head of the Mayor's Office for Policing and Crime to explain the cost and role of the aircraft.
But last month the mayor replied:
For operational security reasons, it is not appropriate for MOPAC to respond.
The video below shows the same plane taking off earlier this year in Cambridge.
Caroline Pidgeon, a Liberal Democrat member of the London Assembly said:
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.