The Ministry of Defence 'doesn't know' the location of 'most' of the military veterans who would be recalled back to service at the time of national danger. 

The military's strategic reserve is made up of around 95,000 soldiers and officers, yet a key government adviser claimed officials have failed to keep an up-to-date contact list for the personnel. 

Former Nato chief George Robertson, who co-chaired last year's strategic defence review (SDR), claimed the revelation at an event in Salisbury, Wiltshire, this week.  

The Labour peer and former defence secretary, as reported by a national newspaper, said: 'What the review talks about is having the strategic reserve, that is, all of the people in this room who've been in the forces who have got a continuing obligation. 

'But the Ministry of Defence at the present moment doesn't even know where most of them are. So we need to sort of round up those who are available and fit and willing to be able to do it.'

Lord Roberton's claim emerged as he said national security had been left 'in peril' by Labour's failure to increase defence spending. 

The Labour grandee told the audience in Salisbury: 'The cold reality of today's dangerous world is that we cannot defend Britain with an ever-expanding welfare budget.' 

Currently under law, all former officers, regular and reserve, can be recalled back to the military during their life. 

The Military of Defence keeps in contact with veterans in the first six years after they have left full-time service through an 'annual reporting' letter. 

The letter is sent on the anniversary of their discharge from the regular army, while the responsibility lies with the personnel to ensure their details are kept current. 

It is understood that records have not been kept updated for a larger cohort of personnel who left the military more than six years ago - with claims the practice has been neglected since the end of the cold war. 

The SDR included recommendations last June that the Government should urgently focus on raising numbers within the strategic reserve. 

Plans were suggested to map the locations and skillsets of reservists and to 'make a more concentrated effort to engage them under a refreshed veterans' communications strategy'.

This comes as the military has struggled to recruit and retain personnel in recent years, with numbers shrinking from more than 100,000 personnel in 2010 to around 70,000 today. 

In efforts to increase numbers, the Military of Defence made attempts to increase reserve numbers by raising the maximum recall age for veterans from 55 to 65, in force from next year. 

As part of the Armed Forces Bill, the legal threshold for recall will also expand to include 'warlike operations' instead of purely an 'actual attack' on the UK.

The move forms part of the Armed Forces Bill and aims to encourage more individuals to enroll into the reserve forces. There are around 32,000 active reservists, both part-time and full-time, in the Armed Forces. 

The Government faced further criticism by Lord Robertson this week over its prioritisation of welfare spending over security. 

He accused Rachel Reeves of blocking funding for the Armed Forces and urged ministers to free up cash by slashing the bloated benefits budget. 

The Labour Peer said: 'Britain's welfare budget is now five times the amount we spend on defence. So I ask, are we certain that this is the right priority – jeopardising people's future safety and security, while maintaining an increasingly unsustainable welfare bill?'

He added: 'We are underprepared. We are underinsured. We are under attack. We are not safe...Britain's national security and safety is in peril.' 

Lord Robertson was backed by fellow Labour peer Lord Hutton, who served as both defence and work and pensions secretary in the last Labour government.

Lord Hutton urged Sir Keir to grip the issue as the 'defining moment in his premiership', saying he has 'a very, very short period of time to start putting this right and sending out the signals to Vladimir Putin' that Britain is serious about defending itself.

He told Times Radio that the Government has 'got to get a grip on the rising welfare budget'. But he warned that, almost two years in, 'there's no real sign that it's got any agenda for correcting the very steep rise in welfare payments'.

It emerged this week that the Treasury is pushing the Ministry of Defence to find £3.5billion in cuts this year – almost the exact cost of the Chancellor's decision to scrap the two-child benefits cap.

Kemi Badenoch said Labour's dithering on the issue was now an 'existential' problem for the country, saying: 'We have got to spend more on defence.'

The Conservative leader added: 'The Government does not have a defence investment plan. There is a welfare plan that runs to 2031 but no defence plan.'

A Military of Defence spokesperson said: 'We recognise the importance of the Strategic Reserve, which is why we are delivering on the Strategic Defence Review through our Armed Forces Bill.

'The Bill will expand our pool of Reserves by increasing the maximum age limit for recall, enable seamless transfer between regular and reserve forces and give the Defence Secretary power to authorise recall for warlike operations.

'We are also constantly improving our data and communicating with our Strategic Reserve community to mobilise talent rapidly when it matters most.'