Parents are being urged to get their children fully vaccinated against polio after samples of the virus which can cause paralysis were found in routine testing of sewage from north and east London.

The tests are done every two weeks from sewage samples from the Beckton treatment works which looks after a population 4 million Londoners, including Barnet residents.

The first samples were found in February and then again in April. No cases of paralytic polio have been discovered and health experts warned people to get vaccinated.

The last case of polio in the UK was in 1984.

The UK Health Security Agency has alerted the World Health Organisation and has increased its testing of wastewater.

Further tests are being done in six areas and results are expected soon.

It is thought that the virus experts found could have come from close contact within a family.

Experts also contacted healthcare workers and doctors to be alert and look out for symptoms of polio, although they are not expecting any cases.

On average one to three viruses are found a year in the UK from testing sites in London and Glasgow.

Dr Vanessa Sailba, consultant epidemiologist at the UK Health Security Agency said finding the samples of vaccine-derived poliovirus is rare and the risk to the public overall is extremely low.

She urged people to make sure their vaccines are up to date as people who are unvaccinated could be at risk.

Three doses of vaccine are given, with the first to toddlers, with a pre-school booster at three years and four months  and boosters for 14-year-olds.

Vaccine rates in London are around 90% but have seen a slow decline in uptake over the last decade.

She said: “Vaccine-derived poliovirus has the potential to spread, particularly in communities where vaccine uptake is lower. On rare occasions it can cause paralysis in people who are not fully vaccinated so if you or your child are not up to date with your polio vaccinations it’s important you contact your GP to catch up or if unsure check your red book.

“Most of the UK population will be protected from vaccination in childhood, but in some communities with low vaccine coverage, individuals may remain at risk.”

London’s chief nurse Jane Clegg said the NHS will get in touch with parents of under fives whose children are not up-to-date with their Polio vaccinations to invite them to get protected.

She said: “The majority of Londoners are fully protected against Polio and won’t need to take any further action.”

She added: “Parents can also check their child’s vaccination status in their Red Book and people should contact their GP Practice to book a vaccination should they or their child not be fully up-to-date.”