Doctors are demanding a halt to a new computerised cancer screening system amid fears it undermines patient care.

A national, paperless programme for cervical cancer tests is due to be launched in Scotland in five weeks.

However, GPs say hundreds of staff have to be trained to use the system, there are issues with equipment and there is no back-up if the technology goes wrong.

Calls for a delay while the process is reviewed are to be put to doctors across the country at a British Medical Association conference in Glasgow next week.

However, NHS managers say the new process will be safer for patients and more efficient.

Women aged 20 to 60 are currently called for cervical smears every three years under arrangements organised by their GP surgery or regional health board. Problems with this were raised almost 10 years ago in a report that found procedures were inconsistent across the country.

From May 28, letters inviting women for cervical cancer checks will be dispatched by one central bureau and GPs will no longer send paper forms to laboratories with each patient's specimen. Instead, they will log details into a computer program, print a barcode and stick this on the top.

GP Jim O'Neil, a member of Glasgow medical committee, said: "We do not have a problem with a national call and recall system, which is a great idea. Our concern is with the additional things they insist happen that are not friendly to the way practices work and we think are probably dangerous to patient care."

In Glasgow alone, 1000 staff have to undergo the two-hour training package in order to work the new software, according to Dr O'Neil.

There are concerns about the compatibility of the different equipment required to produce the barcode labels and, he said, doctors have been told they cannot revert to the paper system if the computer program crashes.

Scotland's most vulnerable women, who do not take up routine offers of screening, are most likely to miss out under such circumstances, he said.

The proportion of eligible women undergoing smear tests in Scotland has fallen in the past decade from 81.7% in 2001-02 to 78% last year. Meanwhile, cancer of the cervix remains a killer. In 2005, 127 women in Scotland died of the disease.

Patients will still receive their test results by letter, but Dr O'Neil said GPs would no longer receive a paper record and will have to access the computer program to know if someone has an abnormal result. "There's just a risk we may not find it, or see it or even look for it," he said. "Glasgow GPs are worried about this . . . We think it is being rushed. We think May 28 is too soon and we need to iron out the problems before it happens."

Calls for a postponement follow a fiasco with the computer program used to shortlist junior doctors for new posts.

NHS National Services Scotland (NSS) said the software was "state of the art" and in the event of isolated IT problems surgeries could revert to a paper request form. They also said the training programme had been available to practices since January.

"The Scottish Cervical Call Recall System has been developed in consultation with stakeholders such as GPs," they said, adding it would cut administration and save surgery staff time.

Pamela Morton of Jo's Trust, a cervical cancer charity, said: "What I would have concerns about is that through no-one's fault some poor women are left out and I would worry about the consequences if they were missed."