Keir Starmer hits back at ex-Nato chief after attack on Labour's defence plans

The spokesman added: "Our armed forces are working around the clock... Our armed forces are among the best in the world and work 24/7 to keep us safe – we have made the largest defence investment since the Cold War."

Lord Robertson, a former Nato chief and co-author of last year's Strategic Defence Review (SDR), delivered a string of criticisms towards the Government over its delay in publishing their Defence Investment Plan (DIP).

In an interview with the Financial Times, the former Labour Defence Secretary referenced the "ever-expanding welfare budget" as a reason why we cannot "defend Britain".

Serving as the military alliance's general secretary from 1999 to 2003, Lord Robertson is also expected to issue a damning verdict on the state of the armed forces at a speech in Salisbury today.

"We are underprepared. We are underinsured. We are under attack. We are not safe," he is expected to say.

However, the Prime Minister's spokesman said the DIP will be "published as soon as possible", further emphasising that Sir Keir is "working to finalise" the plan so that it suits the security needs of the country.

The chair of the House of Commons Defence Committee called Lord Robertson's comments "sobering".

Tan Dhesi, Labour MP for Slough, said: "Lord Robertson's public intervention is sobering.

"It is damning that a man of his stature and experience has to speak out publicly to get his message heard.

"When it comes to defence, the Government's rhetoric promising action does not yet align with reality."

In the SDR, Lord Robertson, alongside the other authors, General Sir Richard Barrons and Dr Fiona Hill, acknowledged that "words such as 'transformation' have been used before in defence reviews but the intention has seldom been delivered".

The DIP was supposed to be published last Autumn, shortly following the SDR.

However, the plan remains on the Prime Minister's desk, creating growing concern among Westminster.

Lord Robertson's comments came after Kemi Badenoch yesterday demanded the publication of the defence plan in the House of Commons.

She said the DIP was "nowhere to be seen" and called upon Sir Keir to find a way to increase defence spending before the end of the Parliament.

It is understood that the Ministry of Defence, the Treasury and No10 are currently at a stalemate over the plan.

Lord Robertson will also take aim at Treasury officials in his speech today, saying the ones with no military experience are causing "vandalism".

He will continue: "There is a corrosive complacency today in Britain's political leadership.

"Lip service is paid to the risks, the threats, the bright red signals of danger—but even a promised national conversation about defence cannot be started."

Defence spending last year stood at 2.3 per cent of GDP, roughly £66billion.

The Government has committed to reaching its three per cent target by the end of the next Parliament, moving further to 3.5 per cent by 2035.

Sir Richard, one of the SDR's other authors, agreed with Lord Robertson's sentiments.

He told the BBC: "There's an enormous gap between where we have to be to keep the country safe in the world we now live in and where we actually are."

The SDR said that the UK faces multiple, direct threats for the first time since the Cold War and that a "step change in the threats we face demands a step change in Britain's defence".