Scientists have decoded human DNA

But pressure groups say that the "genetic identity cards" could lead to discrimination without much benefit to the citizen.

Sir Paul Nurse, the chief executive of Cancer Research UK, predicts that the process of unravelling a human genome could be completed far more swiftly in future.

We need to be extremely careful how this technology is used to shape our society Sir Paul Nurse, Cancer Research UK

This, he said, might eventually help predict vulnerability to common diseases - and help individuals avoid illness by taking preventive measures.

'Gene underclass'

But Sir Paul said that the advances risked leading to "genetic apartheid" as insurers and employers ruled out people with genetic "defects".

Sir Paul, awarded the Nobel Prize for Medicine in 2001, said: "In 1985, it took three years to decode a single gene - now we can sequence the entire human genome in just a few years.

"The American scientist Craig Venter is already offering the very rich to buy a map of their genomes at a staggering $710,000 (£450,000), but even he anticipates selling them for much less in years to come."

Combination of factors

He said some genetic tests - for less common conditions such as Huntington's disease and cystic fibrosis - could predict future disease with some accuracy.

But he insisted more common diseases such as cancer and heart disease were likely to be the result of a combination of many different genes alongside lifestyle factors such as poor diet or smoking.

He said: "We need to be extremely careful how this technology is used to shape our society - this issue is too important to be left to scientists and policy makers alone."

Dr Helen Wallace, from the pressure group Genewatch, said that the public was being "misled" by promises that a map of their genome could offer certainty about their future health.

"Although gene tests can be very useful, there is no way you could use them to predict common disease."