Chris Mason: The tricky trade offense and big numbers Burnham could face soon.

Andy Burnham is expected to inherit a £4.7bn bill to deliver the Defense Investment Plan, or DIP, if he becomes Prime Minister next month, before worrying about how to boost defense spending as the next general election looms.

The numbers accompanying the much-delayed plan indicate a large gap that the current government will need to fill next fall.

Already, the sharp move to get the DIP out the door has sparked controversy, with serving minister Hamish Falconer now publicly voicing his frustration at the uncertainty swirling around the A46 Newark bypass road widening project near Lincoln.

Achieving a £5bn-thick edge from current budgets may require a lot more backbench gnashing of teeth.

Sir Keir Starmer was in a glowing mood when the DIP was unveiled as it took public ownership.

He was waiting for the pledge to be published ahead of next week’s NATO summit in Ankara, Turkey, which was his last scheduled appearance as foreign minister.

Heading there without it would be all the more embarrassing for someone who is already headed for the fire exit of leadership.

But his new defense secretary, Dan Jarvis, was willing to call off the deal, saving Burnham from publishing the publication in just a few weeks.

Over the past two years watching Sir Kerr as Prime Minister, he has always sought to publicly demonstrate the brutal trade-offs he faces. All prime ministers face them, but perhaps this one more than most.

An anemic economy, a high tax burden, a high national debt, a looming benefit bill and huge additional demands for defense spending are the combination.

His first attempt to reform the welfare system was rejected by his own parliamentarians, and the challenge proved difficult.

Well, it won’t be his challenge for much longer.

As Sir Kerr put the DIP, his tone and language were sensitive to the issue: The prime minister who leaked the numbers, investigated the business scandal, because that’s his job.

“There will always be those who say, no matter what the sum is, it’s not really enough,” he told us.

He admitted it was “the end of my journey” but said: “I will leave the stage … knowing that we have put this country in a better place. Are there misunderstandings between departments and the Treasury?”

“Yes, of course they are, they always are, they always will be. At the end of the day, the prime minister and the chancellor have to prioritize the overall judgments of the government, the overall capacity, and among other things.”

Good luck Andy said, it’s harder than it looks.

But instead, that felt like a subtext.