Pigeon patrol takes flight to tackle London's air pollution crisis

Flock of racing pigeons equipped with pollution sensor and Twitter account take to the skies in bid to raise awareness of capital's illegally dirty air

They've been driven from Trafalgar square for being a nuisance, derided as rats with wings and maligned as a risk to public health.

But now pigeons could play a small part in helping Londoners overcome one of the capital's biggest health problems - its illegal levels of air pollution blamed for thousands of deaths a year.