Researchers at the Wellcome Trust say the problem is due to insurance companies failing to understand genetics rather than because of an overall policy of discrimination.

But insurance companies deny this is the case.

The researchers say up to 13% of people who have genetic disorders, are carriers of disorders or have children who have a condition caused by a genetic mutation may be facing unfair discrimination by insurers.

The issue is of particular concern, given that scientists are developing a range of tests which can predict susceptibility to genetic disorders.

Questionnaires

They sent questionnaires to members of genetic disorder organisations and conducted a general omnibus survey.

Each group were asked only if they had experienced problems obtaining life insurance.

A third of the genetic disorder group said they had problems getting insurance, compared with just 5% of the omnibus group.

Under the Disability Discrimination Act 1995, insurance companies are allowed to discriminate on the basis of actuarial or medical reports which predict whether potential clients are likely to die young.

However, the research found that up to 13% of people in the genetic disorder group had problems which were not based on these grounds.

They included people who were healthy carriers of genetic disorders such as cystic fibrosis, healthy non-carriers of late onset disorders such as Huntingdon's disease and the parents of children whose condition is the result of the spontaneous mutation of genes, such as tuberous sclerosis.

Inconsistency

Writing in the British Medical Journal, the researchers say: "The results show that people belonging to support groups for families with genetic disorders were not treated consistently by insurers.

Diseases like Huntingdon's cause progressive brain degeneration

"That there is no clear pattern may be the most important finding; it suggests error on the part of insurers rather than a coherent industry-wide policy of genetic discrimination."

The researchers say this tallies with American research.

"Our findings suggest that in less clear cut instances, where genes confer an increased susceptibility rather than 100% or zero probability, some people might be charged high premiums that cannot be justified on the actuarial risk they present."

They call for further research and more monitoring of the insurance industry.

However, the Association of British Insurers, which has issued a code of practice on genetics, denies there is discrimination.

A spokesman said: "We would be very strident in denying there is discrimination."

He added that the research only showed that people believed they had been discriminated against.

He said the code of practice sets out how insurance companies should deal with genetic test results to ensure people were not deterred from having them.

The code of practice was developed with leading geneticists and has been ratified by the government.

Monitoring

The government is believed to be setting up an independent evaluation scheme to monitor insurance companies' use of genetic test results.

The Human Genetics Advisory Commission has recommended a two-year moratorium on using genetic test results for all forms of insurance while the issue is being debated.

The Cystic Fibrosis Trust said it has a list of insurance companies who are aware of genetic issues which it recommends to its members.

"Some insurance companies do not know enough about genetic disorders," said a spokeswoman.

Cystic fibrosis is the most common genetic disorder. Many people carry it without knowing.

For the condition to develop, a child must receive the defective gene from both their parents. It affects the breathing and can lead to fatal lung infections. The average person with CF survives until they are 31.

The symptoms of Huntingdon's disease usually become apparent at the age of 40. The disease causes brain degradation, dementia and muscular spasms. Most people die within 14 years of the onset of symptoms.

Tuberous sclerosis causes benign tumours to appear all over the body, leading to epilespy, autism and other conditions which can be life-threatening.

Simon Hughes, Liberal Democrat Health spokesman, said: "There is a fundamental principle at risk here. It appears that individuals feel discriminated against by insurers using genetic information to refuse life insurance. If true, this is an attack on the freedom of the individuals involved.

"I hope there is not systematic discrimination by insurance companies. The Government has tentatively suggested an independent evaluation system. This is simply not good enough."