Large numbers of children have not had the MMR (measles, mumps, rubella) vaccine, largely because of the scare that followed the publication of research by Andrew Wakefield in the Lancet medical journal in 1998 that postulated a link between the jab and autism. The research was later discredited and Wakefield was struck off by the General Medical Council for fraud.

In Wollaston's constituency of Totnes, Devon, the concern generated by Wakefield lingers on and is part of the reason, she believes, for a general distrust of vaccines and a reliance on homeopathy – remedies that are almost entirely water.

About 70% of five-year-olds in Totnes were fully protected against measles last year, she said on her blog, compared with 94% of those in Brixham, just miles away.

"Some parents have an unshakeable belief that homeopathy boosts their child's immune system. They would rather put their faith in 'natural' methods, as they see it," she told the Guardian.