All children aged one to nine will be offered a polio vaccine after the virus was found in 116 sewage samples.

Vaccine-derived poliovirus has been detected in sewage in Barnet, Brent, Camden, Enfield, Hackney, Haringey, Islington and Waltham Forest.

There have been no confirmed cases yet but 116 type 2 poliovirus (PV2) isolates were identified in 19 sewage London samples collected between February 8 and July 5.

Most are vaccine-like virus and only a few have sufficient mutations to be classified as vaccine derived poliovirus (VDPV2). VDPV2 is of greater concern as it behaves more like naturally occurring "wild" polio and may, on rare occasions, lead to cases of paralysis in unvaccinated individuals.

Dr Vanessa Saliba, consultant epidemiologist at UKHSA said: "No cases of polio have been reported and for the majority of the population, who are fully vaccinated, the risk is low.

"But we know the areas in London where the poliovirus is being transmitted have some of the lowest vaccination rates. This is why the virus is spreading in these communities and puts those residents not fully vaccinated at greater risk."

The NHS will be contacting parents of eligible children aged one to nine.