The British Army has halted use of its Ajax fleet after dozens of soldiers fell ill due to noise and vibration problems. The embarrassing revelation is the latest controversy in the troubled £6.3 billion Ajax programme and comes just weeks after it was declared safe and ready to fight.

Some soldiers were reportedly left vomiting after taking part in drills inside the armoured fighting vehicle. Thirty-one soldiers from two regiments — Household Cavalry and Royal Lancers — are said to have reported being unwell after spending 10 to 15 hours inside Ajax. The Ministry of Defence (MoD) said a two-week pause on using the vehicles has been ordered as an investigation is carried out.

The troops who fell were taking part in an exercise on Salisbury Plain, Wiltshire, over the weekend.

Sources told The Times that in addition to soldiers vomiting, others were shaking so much they could not control their bodies.

Some also experienced weakness in their legs, it is claimed.

An MoD spokesperson said some of the troops are still receiving medical care.

The news casts serious doubts over the programme which recently received approval to deploy on operations — eight years behind schedule. In early November, Defence Procurement Minister Luke Pollard insisted Ajax was safe and had “overcome” its difficulties.

“We would not be putting it in the hands of our armed forces if it were not safe,” he told reporters during a visit to the General Dynamics plant in Wales, where the vehicles are assembled.

Ajax has been blighted by problems, most notably noise and vibration issues which injured soldiers during testing. Some have been medically discharged, while others have undergone treatment for hearing loss.

Ajax is the first new armoured fighting vehicle to enter service with the Army in almost 30 years. Around 170 of the vehicles have been delivered, with the fleet set to grow to 589 by 2030.

An MoD spokesperson said: “The safety of our personnel is our top priority. This weekend a small number of soldiers reported symptoms of noise and vibration, having taken part in an exercise involving the Ajax armoured fighting vehicle.

“The Army immediately stopped the exercise and proactively tested all personnel involved for symptoms. Upon testing, around 30 personnel presented noise and vibration symptoms. That vast majority of these have now been medically cleared and are continuing on duty. A small number of personnel continue to receive expert medical care.

“Out of an abundance of caution, the Minister for Defence Readiness and Industry has asked the Army to pause all use of Ajax for training and exercising for two weeks, while a safety investigation is carried out into the events this weekend. A small amount of testing of the vehicle will continue, in order to ensure that any issues can be identified and resolved.

“This pause underlines our absolute commitment to the safety of our personnel. As with any major equipment programme, we continue to test and refine the vehicle to ensure safety and performance.”