This means a total of 11 out of 31 suspected cases in Lambeth, Southwark and Lewisham have now tested positive for the virus.

A further 18 children are still under investigation and two tests have come back negative.

There have also been confirmed cases in the north east of England.

The results come as the government attacked "media hysteria" over the controversial MMR triple vaccine - and warned that lives are being put at risk as fewer children have the jab.

Prime Minister Tony Blair's official spokesman called for some "perspective" on the issue, adding that it should not be a "political football".

Let's not plant doubts in peoples' minds... all the medical experts are categorical about this - they say that MMR is the safest option

Yvette Cooper

Shadow health spokesman Liam Fox said, whether rightly or wrongly, the public had lost confidence in the government's policy on MMR - the controversial measles, mumps and rubella vaccine.

He wants parents to be given the choice of a single vaccine.

He said: "In the circumstances I think that reluctantly we have to accept that single jabs may be the only way of giving children protection."

However, public health minister Yvette Cooper defended the MMR vaccine.

She said: "Let's not plant doubts in people's minds because that is not the situation here.

"All the medical experts are categorically about this - they say that MMR is the safest option."

Poor MMR uptake

Lambeth, Southwark and Lewisham has a very low uptake figure for the controversial Measles, Mumps and Rubella (MMR) vaccine.

In the quarter leading to September 2001, only 65% of eligible toddlers were immunised.

Toddler Clara Forbes - one of the 11 - had to be rushed to intensive care after developing the virus last month.

In the circumstances I think that reluctantly we have to accept that single jabs may be the only way of giving children protection

Dr Liam Fox

She is now recovering, although her mother Hazel said that her condition had been "touch and go" with initial fears that the virus could move to her brain. On average, there are fewer than 100 cases of measles nationally each year. Although the 2001 figures are not yet complete, 61 cases have so far been confirmed in that year.

The 22 children under investigation had symptoms which could be early signs of measles, but which could also be signs of other conditions.

Some in this group are also believed not to have the MMR jab.

Yearly figures from the Public Health Laboratory Service for the year from April 2000 to March 2001 showed 73% of children in Lambeth Southwark and Lewisham had been vaccinated before their second birthday.

The figure for 1990 to 2000 was 76%.

Recommended coverage levels are 90% - the national average is approximately 84%.

MMR can protect 90% of all children who have had the first vaccination, a second dose raises the level of protection from measles to 99%.

Measles is potentially dangerous in a very small number of cases - it can lead to pneumonia or brain swelling.