Sir Keir Starmer has warned his likely successor Andy Burnham will have to spend just as much time dealing with global turmoil as he has during his time in No 10.

In an untypically candid interview, the outgoing prime minister spoke for the first time about the “intensely personal” and “really tough” decision he took alongside his wife and children to accept that his “political career” was “over”.

Sir Keir told the BBC he had “saved” the Labour Party and been a successful prime minister.

He promised to “keep my mouth shut” under his successor, insisting that he liked Burnham and the pair had “always got on”.

Sir Keir has faced frequent criticism during his two years as prime minister – an anniversary he is marking this weekend – about the amount of time he has spent on the world stage, with critics labelling him “never here Keir”.

Among Burnham’s supporters in parliament are those who hope he will be able to focus more on issues in the UK such as the cost of living and public services.

“It is not sensible to think you can just separate these two things out,” Sir Keir said.

Asked if a prime minister could spend less time on diplomacy than him, he replied: “No, I don’t think it is possible.”

He added: “There’s often this discussion – what’s the right balance between dealing with international affairs and dealing with domestic affairs? They’re one and the same thing.”

Sir Keir continued: “Whoever’s my successor is going to face the same global conflict. We keep saying, and it’s true, we’re in a more dangerous and volatile world than we’ve been in for probably most of my lifetime. That’s not just a phrase, that’s reality.

“That’s not going to change. And the domestic challenges aren’t going to change.”