A mother who says her two youngest sons developed autism after being given the MMR vaccine is taking part in a national protest.

Isabella Thomas, from Newhaven, is a member of the Justice, Awareness and Babies Support group (JABS).

She is one of hundreds of parents and children taking to London today in a bid to persuade the Government to help autistic children whose parents claim they became ill after being given the measles mumps and rubella vaccine.

The march will culminate with a petition being handed to Number 10 Downing Street by nine-year-old Thomas Hewitt, from London, who is autistic and has the measles disease in his body.

Similar marches will take place on the same day in Edinburgh, Cardiff and Dublin.

Mrs Thomas, whose two youngest sons, Michael, 10, and Terry, 8, are autistic, said: "We are asking for urgent help.

"It is no good saying to us there is no proof autism and the MMR jab are connected because whatever has caused our children's condition has made them very sick and their conditions are being ignored.

"Figures show 20,000 children in the past 12 years have developed autism. Until 1990 it was very, very rare and now it is more common.

"I am 100 per cent sure my sons' conditions were caused by the MMR jab.

"On the day Michael had the jab, within two hours he was seriously ill. At the time it was not heard of and I was told by doctors it was a coincidence.

"There was a lot of pressure on me when it came to Terry to have it done so I gave him the jab and that night he had a fit.

"Michael now hallucinates, gets serious headaches and mental blackouts and has breathing and eye problems.

"Both suffer from crippling stomach cramps and bowel problems."

Mrs Thomas has two older sons, aged 24 and 21, who were not given the vaccine. They are not autistic.

She said: "JABS hears from parents every day looking for information and advice."

The march will begin at Whitehall Place at noon and arrive at Downing Street at about 1pm.