British forces have lost 19 of the special, high-mobility Wimik Land Rovers delivered to Afghanistan's Helmand province last summer in action against the Taliban.

Although the Ministry of Defence refuses to disclose the total number deployed, military sources say the losses represent about one in six.

Five soldiers are known to have died on the unprotected vehicles after they were caught in the blast of roadside bombs and an unknown number have been wounded. At least one, a member of the elite Parachute Regiment, lost a leg.

The Wimik (weapons-mount installation kit), a Land Rover stripped of its armour and fitted with a 50-calibre heavy machinegun and a 7.62mm medium gun, was introduced to provide both firepower and rapid cross-country performance for the UK task force.

While specialist troops such as the SAS are happy with the vehicle in its off-road role and prepared to trade protection for speed and hitting power, regular battalions forced to use it for supply convoy escort duty complain that it leaves its crew exposed to rifle fire.

An MoD statement said: "Weapons-mount installation kit Land Rovers were first deployed to Afghanistan in summer, 2006. We can confirm that a total of 19 have been lost as a result of operational use.

"Those losses have occurred either as a result of direct enemy action or denial operations by UK forces where those vehicles have been extensively damaged and cannot be recovered.

"Five personnel have been killed in Wimik Land Rovers since last summer. Those deaths all occurred where the vehicles were involved in an explosion due to enemy action."

An officer with extensive combat experience in Afghanistan told the Herald: "The vehicles are fine as long as they are used in the role for which they were intended. They are not suitable for escorting resupply convoys, since the crew is totally exposed to any kind of enemy fire, especially mines and bombs." He added: "The fundamental problem is that we have too many senior people who still think we're the Long Range Desert Group fighting the German Afrika Corps in the desert. And too few vehicles for the tasks in hand, meaning that the Wimiks and their crews are used for routine jobs, which leave them vulnerable to bombs, mines and gunfire."

Sources say troops have begun to fit improvised armour to help reduce the risks.