All trials involving the Ajax armoured vehicle have been suspended again, due to renewed concerns over noise.
Tests of the programme were previously "paused as a precautionary measure" between November 2020 and March 2021.
It was confirmed earlier this month that some crew members involved in the trials were continuing to receive medical attention after concerns were raised over "noise and vibration levels".
The Ministry of Defence (MOD) said in a series of tweets that the trials will only resume "when we are assured that mitigations are fully effective".
On Tuesday, in response to a written question about the numbers of personnel injured during the testing of Ajax armoured vehicles, Baroness Goldie, Minister of State for Defence, said "21 incidents of hearing treatment have been recorded".
She added "as a precaution, a further 83 soldiers... will receive annual hearing tests" – despite not showing any signs of hearing loss.
"Trials resumed in May 2021 with restrictions on use and extra hearing protection mandated," she said.
"Notwithstanding these measures, this month, two soldiers reported symptoms of noise-induced hearing loss, with one more being assessed."
Baroness Goldie also said five soldiers had reported to "their local medical centre with vibration-related symptoms", but did not require further treatment.
"There have been no reports of injuries requiring hospital treatment," she said.
On Tuesday, Minister for Defence Procurement Jeremy Quin visited the Millbrook Proving Ground where independent testing has been conducted on Ajax.
"This long-running troubled programme requires ongoing intense work by our industrial partners and ourselves to ensure its delivery," he said.
"In achieving this, the safety of our personnel will always come first."
Earlier in June, Mr Quin admitted there are "serious issues" with the Ajax programme, before revealing there were "anecdotal reports of vibration" following the involvement of soldiers in pre-trials training on prototype variants of the vehicles in 2019.
The defence minister also stated "headsets" were being considered for use with the trials, but added: "That does not get us to the root cause and we need to get to the root cause of the noise issues within this vehicle, be that mechanical or, indeed, electronic."
Watch: 'We need to get to the root cause': defence minister on Ajax issues, earlier this month.
On Wednesday morning, the chair of the House of Commons Defence Select Committee, Tobias Ellwood MP, called for the project to be "scrapped" citing growing costs for each individual vehicle.
Writing on Twitter, he said: "Cost now exceeding £7m per vehicle.
"MOD should draw a line to resolve current issues, beyond which, the project should be scrapped.
"Plan B could follow the US Marines’ example and move to a wheeled recce vehicle (with a Turret) such as BOXER."
Earlier this month on 17 June, in response to a written question regarding the delivery timetable of Ajax, Baroness Goldie said the forecasted Initial Operating Capability (IOC) was 30 June 2021.
She said there was "50% confidence" in the June delivery date and "a 90% confidence for September 2021".
"To be clear the department will not take the programme into IOC until we are confident that we have achieved what we need to achieve at this stage of the vehicle's development," she said.
"The contract with General Dynamics Land Systems UK is a firm price contract to deliver the requirement in a set budget."
What is the Ajax?
To date, 14 Ajax vehicles have been delivered to the MOD, including the Ares variant, which is designed for reconnaissance and troop-carrying.
Ajax will be a fully digitised, tracked, medium-weight core of the British Army's deployable intelligence, surveillance, target acquisition and recognition (ISTAR) capability.
Cover image: The 'Overwatch' Ajax variant (Picture: General Dynamics Land Systems).