The report, published in medical journal Cancer Research, suggests that current research could lead to women taking a simple blood test for screening, combining with other factors such as family history and the presence of other cancer genes.

The test will look at how far genes are altered by factors such as alcohol and hormones

One in five women is thought to have what is referred to as a genetic “switch”, which doubles the threat of breast cancer.

Scientists studied 1,380 women’s blood samples for the research and 640 of those went on to develop breast cancer. They managed to find a strong link between breast cancer and molecular modification in the white blood cells.

In some cases, the change in molecules was clearly visible 11 years before the breast cancer was diagnosed.

The man who led the research, Dr James Flanagan, said: "We know that genetic variation contributes to a person's risk of disease. With this new study we can now also say that epigenetic variation, or differences in how genes are modified, also has a role.

"We hope that this research is just the beginning of our understanding about the epigenetic component of breast cancer risk and in the coming years we hope to find many more examples of genes that contribute to a person's risk.”