When you're taking on something like the establishment... then you are inevitably going to come up against this kind of issue

Dr Andrew Wakefield

From the moment he first voiced concerns over MMR, Andrew Wakefield has faced intense criticism from the Department of Health and the medical establishment. Reports from two expert committees have insisted the MMR vaccine is safe.

The pressure on Dr Wakefield to produce the evidence has been intense. But it seems to have made him even more determined to carry on.

"When you're taking on something like the establishment on the issue of the safety of a vaccine that has been hailed as being extremely safe, then you are inevitably going to come up against this kind of issue," he said.

Safety tests

In January 2000 Dr Wakefield published a new paper that questioned whether the MMR vaccine had ever been properly tested for safety.

Dr Miller: MMR vaccine not linked to autism

He claimed the tests were too short to pick up long-term problems like autism. This highly controversial paper created another media storm and more confusion about MMR.

Before the study had even been published, the Department of Health went on the offensive. They launched a concerted attack on Wakefield's credibility.

Dr Elizabeth Miller spoke at a government press conference in January 2001. "There are no grounds for suspecting that MMR vaccine causes autism," she said.

Family decision

Dr Wakefield's concerns about MMR have had a direct impact on his family. He and his wife, also a doctor, had to decide whether their own children should be given the triple jab.

Dr Wakefield's wife, Carmel, told Panorama that their first two children were given the vaccine.

"But then as Andy's work was unfolding and the potential link to MMR and problems began to unfold, then we had to reappraise our policy on vaccinating our own children, so our second two children have not had MMR vaccination," she said.

In March 2001, Dr Wakefield went to Washington to give evidence before a Congressional committee investigating the potential link between MMR and autism.

There is no evidence that the onset of autistic symptoms is more likely shortly after MMR vaccine than at any other time

Dr Elizabeth Miller

Dr Miller, the British government's representative, was in the audience to listen to Wakefield's new evidence. She came to present her own new evidence to refute his claims.

"There is no evidence that the onset of autistic symptoms is more likely shortly after MMR vaccine than at any other time," she said.

"Indeed new evidence which is shortly to appear from my colleagues and myself in a vaccine journal is that there is no evidence that MMR vaccine increases the likelihood of autism at any time after vaccination."

Having spoken so publicly about his concerns about MMR there is growing pressure on Andrew Wakefield to produce some proof. Panorama reporter Sarah Barclay separates fact from fiction in the war on words in this important part of public health policy.

Watch 'MMR: Every Parents Choice' at 2215GMT on Sunday on BBC One or via a live stream on this site.