Personnel numbers in some frontline British army units are down by as much as a third, figures show, prompting serious concerns about their readiness for action.

The government was accused of “appalling complacency” over recruitment after the publication of the Ministry of Defence (MoD) data, which showed a number of battalions with hundreds fewer troops than their requirements state.

While publicly available government figures show an overall deficit of 8%, the new data showed a much larger deficit in infantry groups on the frontline.

Information published in response to a parliamentary question by the MP Mark Francois revealed that the Scots Guards, 1st Battalion, only had 460 personnel in October last year, 34% below its 697 workforce requirement. The Princess of Wales’s Royal Regiment, 2nd Battalion, had 330 people, 31% below its target strength.

The Welsh Guards, 1st Battalion, and the Mercian Regiment, 2nd Battalion, had only 72% of their target strength, while the Duke of Lancaster’s Regiment, 1st Battalion, had only 74%.

Twelve of the 30 infantry battalions included in the data were missing more than one in five of their required personnel, while only three met or exceeded their requirement.

Dr​ Jack Watling, a research fellow at the Royal United Services Institute, said the figures were worrying, pointing out that Russian ground forces already had much higher numbers of infantry in equivalent units.

“You need three times as many men as the enemy when attacking,” he said. “A battalion that is missing 10% of its strength can probably compensate for the shortfall. Having lost 30%, you are not going to be able to generate the combat power to stand up to two enemy battalions, even in the defence.”

The British army is on course to miss its targets for the number of recruits it should have by 2020. The army’s 2020 strategy, published in 2015, aimed to have 82,000 army personnel and 30,100 reserves by March 2019. According to MoD statistics, the army only had 79,790 trained personnel in October 2018, and 26,960 trained reserves.

In 2012, the MoD signed a decade-long contract with the outsourcing company Capita to manage recruitment to the armed forces. The National Audit Office found in December that Capita had consistently missed the army’s targets, with the shortfall ranging from 21% to 45% each year.

Responding to the figures, Francois, the Conservative MP for Rayleigh and Wickford and a member of the defence select committee, said: “These numbers make starkly apparent what ministers have been seeking to hide for some time, which is that the frontline strength of the regular army is now being seriously eroded by the lack of recruits to refresh infantry battalions, because of the calamity that is the Capita recruitment contract.

“This has gone beyond the simple criticism of an ineffective contractor: this now directly affects the defence of the realm. These people are so incompetent that they are now impacting our national security and ministers should sack them without hesitation.”

In the summer of 2017, Francois published a report into army recruitment, in which he also attributed the fall in recruits to low unemployment, an ageing population, the increase in people taking up post-16 education and the ending of the deployment to Afghanistan in 2014.

Nia Griffith, the shadow defence secretary, said: “Ministers are guilty of appalling complacency as personnel numbers fall month after month. There is now nothing short of a crisis in recruitment and retention to the army. The decision to outsource recruitment to a private company, Capita, has been a total failure. It is high time to scrap that bad deal and bring the service back in house.”

Watling said the MoD should shorten the bureaucratic process for signing up recruits. “Enough people apply to join, but far too many drop out,” he said. “The MoD also needs to strengthen their offering to enlisted soldiers. We don’t see the same retention problems among officers. Every man who leaves takes their training and experience with them, so we need to improve retention.”

An army spokesperson said it was meeting all its operational commitments to keep the country safe. “The ‘workforce requirement’ is not the minimum threshold the army needs to fulfil its operational requirements, it represents the number of positions in each battalion,” they said. “We are fully committed to improving our recruiting process, and working with Capita, we have put in place a plan to address the challenges.”