The Ministry of Defence recommended the 3,500 personnel deployed to the Gulf earlier this year take anthrax injections.

Nearly 75% fo troops refused jabs

But despite also receiving a personal letter from Defence Secretary George Robertson, who also took the vaccine to calm fears about its side-effects, 73% refused.

The MoD said it was now considering whether to join countries like the United States in making the jabs mandatory.

A spokesman said: "We are keeping this whole area under review. We would not rule out compulsory vaccination in the future."

Anti-biological and chemical warfare vaccines given to troops during the 1991 Gulf War have been blamed for causing outbreaks of mystery illness among veterans.

The anthrax vaccine, offered separately to soldiers and sailors this time around, formed part of that cocktail.

In an attempt to encourage take-up, Mr Robertson, Armed Forces Minister Dr John Reid and Chief of the Defence Staff General Sir Charles Guthrie all had the vaccinations.

1991 injections blamed for Gulf War syndrome

The MoD has admitted that just 28% of total service personnel had the injections, comprising 54% of land forces and 17% of those at sea.

A MoD spokesman said the vaccines had been offered in addition to protection offered by and contamination-proof areas of ships and anti-nuclear, chemical biological warfare suits.

He said: "The vaccines were not compulsory but the recommendation was that they should be taken. They were intended to discharge our duty of care, but it was for the individual to make that decision."