On the latest episode of the Daily Mail’s Deep Dive podcast, defence editor Mark Nicol unpicks the government’s long-awaited Defence Investment Plan (DIP) and the extra £1.5 billion in spending that appears to have been included at the eleventh hour.

On Tuesday, departing Prime Minister Sir Keir Starmer unveiled the plan, intended to spell out how the government would fund the sweeping recommendations made in the Strategic Defence Review (SDR), a document published last year that called for a radical modernisation of Britain’s armed forces.

The military had signalled it needed around £28 billion over four years to deliver that ambition in full. The Defence Investment Plan was then delayed for more than seven months.

On Tuesday, Sir Keir Starmer unveiled the plan, intended to spell out how the government would fund the sweeping recommendations made in the Strategic Defence Review

The Defence Investment Plan: Has Starmer Laid a Trap For Burnham?- Listen to the latest Daily Mail Deep Dive podcast

In that time, Defence Secretary John Healey and his deputy, Armed Forces Minister Al Carns, both quit, after the Treasury reportedly offered just £13.5 billion for defence. Their resignations seriously dented Starmer’s premiership and just days later he announced he would step down from Number 10.

Speaking to Deep Dive host Chris Pleasance, Nicol, despite branding the plan ‘lacklustre’, speculated that had the final figure of £15 billion been offered sooner, it might well have been enough to keep the loyal Healey in post.

Nicol said: ‘Is this an absolutely colossal political misjudgement, even by Starmer’s standards? I think £15 billion would have kept Healey, considering how loyal he is by nature.

‘Did £1.5 billion essentially cost Starmer his job? His own resignation was precipitated by their resignations, the momentum that came from them.

‘In a premiership that will probably be remembered for its U-turns, its wobbles, its misjudgments, this may turn out to be the biggest of them all.’

Elsewhere in the podcast, Nicol claimed ‘treasury tricks’ could be behind Labour’s sudden discovery of an extra £1.5 billion for defence.

A sum that size, he argued, is easily lost in the accounts, useful for covering day to day running costs but small enough to disappear into the bigger picture.

Under the plan, core defence spending will edge up only from 2.6 to 2.7 per cent of GDP by 2030, at a time when NATO wants every member reaching 5 per cent within a decade.

Nicol also voiced disappointment that more had not been redirected towards the technologies proving decisive on the modern battlefield, such as drones, away from what he sees as ageing platforms.

Elsewhere in the podcast, Nicol claimed ‘treasury tricks’ could be behind Labour’s sudden discovery of an extra £1.5 billion for defence

He explained: ‘Carns made the point that 90 per cent of Russian casualties are inflicted using drones, yet out of a package worth around £70 billion a year, we can only find £5 billion for them.

‘The government chose not to involve Al Carns in writing the DIP, and when he finally saw it he was said to be disappointed, because it leant too heavily on legacy systems.

‘Why, for instance, are we pursuing ventures such as the Challenger 3 tank, particularly as a manned capability, when tanks of the future are clearly uncrewed? There’s no need for a human being to be in them.’

Hear Nicol’s full analysis of Labour’s Defence Investment Plan by searching for Deep Dive, wherever you get your podcasts.