The number of confirmed cases of measles in England and Wales rose significantly last year.
MMR vaccination rates have fallen
Provisional figures seen by the BBC indicate there were 310 cases, the highest number seen since the triple measles, mumps and rubella vaccine was introduced in 1988.
It is around three times the number of cases seen in previous years.
Experts say is a "significant rise" in cases, despite the relatively small numbers.
Over 90% of those who contracted measles had not been vaccinated. Three quarters of those affected were children.
It is unlikely we will see large epidemics unless coverage at school-age starts to fall
Dr Mary Ramsay, Public Health Laboratory Service
One in 10 of those thought by doctors to have measles were confirmed as having the disease - double the normal rate.
Around 100 cases were in the Lambeth, Southwark and Lewisham areas of south London, where there was an outbreak of measles early last year.
The MMR vaccination rate in the area is one of the lowest in the country, with just 72% receiving the vaccination.
The figures are due to be published by the Public Health Laboratory Service (PHLS) next month.
Experts say it once again raises concerns that the fall-off in numbers of children having the combined vaccine, will lead to increasing outbreaks of the disease.
Dr Mary Ramsay, an expert in communicable diseases with the PHLS, told the BBC: "Most of the rise is due to the large outbreak in South London which centred on a number of nurseries and primary schools where there were very low vaccination rates.
"But to put this in context, there were 300 cases last year compared to 80,000 in the year before the MMR vaccine was introduced, so its still a very low level."
She warned: "There is a risk of having small outbreaks like the one seen in south London in areas where vaccination coverage is not good.
"But coverage at age 5 is still over 90% so it is unlikely we will see large epidemics unless coverage at school-age starts to fall."
Dr Ramsay said the scientific evidence was "absolutely clear" that there was no link between the MMR jab and autism, but accepted many parents were still not convinced.