Ten pigeons armed with air pollution detectors on their backs were released into the London sky on Wednesday to monitor pollution in the British capital, organisers of the initiative told AFP.

Equipped with GPS devices and pollution sensors to monitor nitrogen dioxide and ozone levels, the birds dubbed the "Pigeon Air Patrol" were released from Primrose Hill, a wealthy area in north London.

The data they collect can be followed on the website pigeonairpatrol.com, said Romain Lacombe, founder of the French start-up Plume Labs, who started the project with Pierre Duquesnoy of DigitasLBi.

The pigeon patrol is part of a wider project by Plume Labs in which 100 Londoners equipped with detectors will monitor pollution in different parts of the capital which can be checked by fellow residents.

Anyone wanting to take part can do so through a crowdfunding platform by buying a place for between �79 and �99 (100 to 126 euros, $111 to $140).

On Wednesday, 60 places had already been snapped up.

Britain's air pollution problem was the focus for tough questioning of Prime Minister David Cameron by opposition Labour leader Jeremy Corbyn in parliament on Wednesday.

Corbyn cited data showing that 40,000 people die in Britain every year because of air pollution, which costs the British economy �20 billion.

A King's College study last year said air pollution had contributed to the death of 9,500 Londoners.

The Labour leader said the "sad truth" was that 500,000 people would die from pollution before Britain manages to attain its obligations to reduce levels -- 15 years after the timetable originally agreed with the European Commission.

London has recorded the highest nitrogen dioxide levels of any European capital and Britain in 2014 was taken to task by the European Commission for failing to meet its obligations.