Professor Mark Caulfield, the project's chief scientist, said: "If there was just one medicine that came out of this programme that would be well worth the investment."
But there are fears that drug companies and insurers will take advantage of research material - and that confidential medical information could be made public. Some campaigners fear it is the first step towards a national DNA database.
The project, which is launched today, aims to read the genetic blueprint, or genome, of around 75,000 volunteers.
This includes patients with breast, bowel, ovarian and lung cancers and leukaemia, and people with rare genetic diseases and their relatives.
With genetic diseases usually striking early in life, many of those taking part will be children. Cancer patients will have two samples read - one from the tumour and one from healthy tissue - taking the total number of genomes read to 100,000.
After the DNA is decoded, the information will be combined with data from the person's medical records, creating a 'lifecourse picture' of the disease.
Patients will be given any information that will help treat their illness. For instance, the data might show that a certain cancer drug is likely to work particularly well or that a child with a rare disease could be given a diagnosis for the first time.
Those who choose to will also receive information about a small number of illnesses that can be seen in their DNA and for which treatments are available.
But they will not be given other information, such as whether they have a gene that puts them at high risk of developing Alzheimer's disease.
The value of genetic testing is demonstrated by Angelina Jolie's experience.
Testing revealed that the Hollywood actress carries a mutation of the BRCA1 gene, meaning she had an 87 per cent risk of developing breast cancer and a 50 per cent risk of ovarian cancer.
The data led Jolie, 39, to have a preventative double mastectomy. Her mother, actress and producer Marcheline Bertrand, died from ovarian cancer at the age of 56.
The NHS, which is ploughing £20 million into the 100,000 Genomes Project, will keep one set of data. A second set will be anonymised and put on a separate database.
Universities and drug companies will be able to access this database and use the information to develop new diagnostic tests and drugs.
Those behind the project say investment from industry is vital if progress is to be made.
Patients with a disease that is of interest will have to consent to their information being shared with industry and can withdraw from the project at any time.
The first to benefit are likely to be children with hard-to-diagnose genetic diseases. Reading their DNA could lead to their condition being named - and treated for the first time.
The information could also be used to tailor cancer treatment to the patient's DNA. For instance, the breast cancer drug Herceptin only works on cancer with a certain genetic flaw.
Crunching data from thousands of people could provide the clues to new tests and drugs including those that prevent disease rather than merely treat it.
Other possibilities include cancer drugs that kill the tumour without harming healthy tissue - sparing patients the ordeal of gruelling chemotherapy.
It could also provide valuable insight into which patients will benefit most from medicines already available - so making better use of the health service's precious funds.
Eleven NHS trusts will take part initially, with 100 new genomic medicine centres established by the end of the three-year project.
- Daily Mail
