Residents are being warned not to touch a breed of caterpillar which is beginning to emerge in oak trees across the capital.

The oak processionary moth pose a health risk because they have tiny, toxin-containing hairs which, on contact, can cause itchy skin rashes in people and animals.

Eye and throat irritations have also been reported as symptoms. They are advised to keep children, pets and livestock away from the caterpillars and their nests, and to report any sightings to the Forestry Commission.

The affected areas are several boroughs in West and South-West London, Bromley and Croydon in South London, and Pangbourne in West Berkshire.

Caterpillars of the oak processionary moth (OPM), which was accidentally introduced to Britain from mainland Europe in 2006, are a tree pest and pose a threat to human and animal health.

They are a tree pest because they damage oak trees by feeding on the leaves, in some cases leaving the trees severely defoliated and vulnerable to other pests, diseases or drought.

Anyone who experiences an itchy or painful skin rash or a sore throat and irritated eyes after being near oak trees in these areas should consult their GP or NHS 111.