More soldiers than ever are using cocaine - and being dishonourably dismissed

The number testing positive for the class A drug has quadrupled since 2003.

Research into compulsory drug testing in the Army found that 769 soldiers tested positive for illegal drugs in 2006 - up from 517 just three years before.

Soldiers who test positive for illegal drugs are usually dishonourably discharged.

The Journal of the Royal United Services Institute, which published the report, said the loss of personnel was higher than the number of fatalities and serious casualties in Iraq and Afghanistan combined.

Christianne Tipping, defence management analyst from RUSI, said: "The issue of an increasing number of drug-related discharges, at a time when recruitment and retention are problematic, needs to be examined by the Ministry of Defence."

The survey comes just weeks after 17 soldiers from the 5th Battalion The Royal Regiment of Scotland (Argyll and Sutherland Highlanders) tested positive for drugs after a rest and relaxation period in Cancun, Mexico.

They were all dismissed.

Professor Sheila Bird, senior scientist at the Medical Research Council, said the Army's cocaine positive rate was probably the tip of the iceberg.

The positive rate is up from 1.4 per 1,000 in 2003 to 5.7 in 2007 - a more than four-fold increase.

But the testing programme is likely to miss infrequent drug use, so cocaine use could be two to three times higher.

In 2003, cannabis accounted for half of all positive tests, compared to 22 per cent for cocaine.

But by 2006, around 50 per cent of all positive tests registered cocaine use, with cannabis around 30 per cent.

A spokesman for the Ministry of Defence said: "Positive drug testing rates in the Army over the last four years average around 0.77 per cent, compared with over 7 per cent in civilian workplace drug testing.

"Drug misuse is significantly less prevalent among service personnel than in corresponding civilian groups."