The Prime Minister will announce £100m has been set aside for the project over the next three to five years. The aim is to give doctors a better understanding of patients' genetic make-up, condition and treatment needs, and help develop new cancer treatments. One human genome contains three billion base pairs - the building blocks of DNA.
Sequencing the code produces a huge amount of data. Although the price is falling fast, it currently costs £5,000 to £10,000 - which explains why no country in the world has embarked on mass DNA mapping on this scale. When it will start - who will do the genome sequencing and analysis - has not been worked out - nor which patients will be eligible for the voluntary testing.
But the hope is by comparing genetic profiles of huge numbers of patients, it will allow scientists to understand why some do far better than others - and help in the quest for new treatments.
Privacy campaigners are concern such a move could allow personal data to be passed on to private companies, such as insurance companies.