Sir Keir Starmer has warned his likely successor Andy Burnham it will not be possible to spend less time focusing on international affairs.
In his first sit-down interview since announcing his resignation, the Prime Minister also spoke of his “intensely personal” decision to quit.
Throughout his premiership, Sir Keir has faced accusations of spending too much time on the world stage instead of domestic affairs, with his opponents branding him “never here Keir”.
Mr Burnham, his likely successor in Downing Street, has largely focused on domestic issues as he sets out his stall to be the next prime minister.
But Sir Keir warned that Mr Burnham will not be able to spend less time grappling with the turmoil around the world than he has.
He told the BBC: “If you’re prime minister and you care what bills are going to be like in any household around the country, you have to care about finding a lasting solution to the situation in Ukraine, you have to care about what happens in the Strait of Hormuz.
“It’s not sensible to think you can just separate these two things out.”
Asked if he believed it was possible for his successor to spend less time on diplomacy, Sir Keir said: “No, I don’t think it is possible. So this suggestion you can really, in the modern era, simply split up the international and domestic, is just… it just doesn’t make sense.
“It isn’t true. It isn’t right.”
Sir Keir also spoke about how he came to the decision to resign, after spending a weekend with his family at Chequers, the grace-and-favour Buckinghamshire country estate available to all prime ministers.
He said: “For me, and this may be different for other people, in the end it became an intensely personal decision, and that’s why it was a decision taken ultimately when Vic and I were away with the kids, we went to Chequers and just spent two days together as a family, and that’s when I came to my final decision.”
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