The unpublished research concludes that the American-style protective vests used by the Metropolitan Police at a cost of pounds 8m are the wrong type for Britain. Other police forces are also understood to be using similar equipment.
The findings from the 18-month study have caused a row with Scotland Yard who argue that the "MetVest" is the best available.
Forces throughout the country have been providing body armour to beat officers following a growing number of attacks.
But a leading medical expert says that the Metropolitan Police equipment is ideal for stopping bullets, but cannot prevent a blade from inflicting a fatal injury. His studies show that officers could be in danger of serious injury to heart, lungs, liver, spleen and kidneys.
He argues that only a tiny number of patrol officers are shot - in the eight years from 1988 to 1995 there were 90 officers shot while on duty, of whom seven died - compared with the relatively large numbers of knife attacks.
In the Metropolitan Police area during 1993 and 1994 two police officers were stabbed to death, 22 seriously injured and 41 received minor wounds. This compares with one fatal shooting and six serious gunshot wounds.
Tony Bleetman, an accident and emergency consultant at Heartlands hospital in Birmingham, said: "The biggest threat to patrol officers is from knives. There's a negligible ballistic threat - ordinary patrol police officers therefore need to be protected from knives first and foremost, not guns."
Under the Home Office standards for body armour the blade of a knife should penetrate no more than five millimetres before being stopped and a bullet can push the vest back 25mm.With the MetVests, a knife can penetrate 20mm and a bullet can push the vest back 44mm.
Mr Bleetman examined whether it was safe to allow a knife to enter the body for 20mm.
He concluded: "If it goes in this far there's a much, much higher risk to injury to heart, lungs, liver, spleen and kidneys. For knives this standard is unsafe, but with 5mm nothing will get damaged."
He added that the vests are very effective at preventing death from shooting.
Mr Bleetman said that there were vests that meet all the specifications but admitted they were more cumbersome. Scotland Yard argues that officers must be able to move easily in the new equipment.
A Metropolitan Police spokesman said: "The MetVest is the best equipment available. We have tested it to our own very high and rigorous standards based on our own detailed risk analysis and we are confident it will be effective against the vast majority of knife attacks which our officers are likely to face."
Mr Bleetman has also examined 500 stabbings in Glasgow and found that armour has "blind spots" where parts of the body are not fully protected. He believes they should be strengthened at the base of the neck, the left side of the chest and the left side of the body, areas where most fatal stabbings occur.
His study discovered that in 7.7 per cent of the cases someone was fatally wounded, about a third of the time they received life-threatening injuries, particularly in the face, neck and abdomen, and in about 60 per cent of cases they received minor wounds, typically slash wounds all over the body.
The research was part-funded by the Police Federation and will be presented at its annual conference in Blackpool later this month.
Mr Bleetman has also considered the effect on women who wear vests and has concluded that there is a short-term risk from inflammation to the breast tissue and "jogger's nipple", caused by friction.
But he has ruled out any links with cancer. He concludes that there needs to be better fitting vests for women, with a wider range of sizes.Reuse content