Donald Trump has suggested Britain should use the military to stop small boat crossings.
The volatile US President told a press conference that unauthorised migration "destroys countries from within". He suggested using the armed forces - implying the British Navy could be deployed in French waters, threatening a face-off with a NATO ally.
Trump rambled that the situations in the UK and US were "very similar", saying: "I told the Prime Minister I would stop it. It doesn't matter if you call out the military, it doesn't matter what means you use. It destroys countries from within. And we're actually now removing a lot of the people that came into our country."
But Mr Starmer said the key to solving small boat crossings lies with co-operating with neighbours. He hailed the first removal of a migrant under the 'one in one out' deal with France on Thursday morning.
The Prime Minister said: "This is a problem right across Europe, to tackle the problem to actually breaking up the gangs who are running this trade.
"We have had a record number of returns - over 35,000 now since we came into office. That's the highest number in the best part of ten years."
Mr Starmer told reporters he was "pleased" the first migrant, an Indian national, had been deported early on Thursday, saying: "That is an important step forward... Given the challenges of returning people, it is important that we're able to prove that can be done.
"It was done, it was done early this morning." And he continued: "We need to ramp that up at scale."
The unpredictable US President, standing alongside the PM at Chequers in Buckinghamshire, claimed to have settled seven conflicts - but accused Russian tyrant Vladimir Putin of letting him down.
He rambled: "The one that I thought would be easiest would be because of my relationship with President Putin, but he's let me down. He's really let me down first on Russia and Ukraine. But we'll see how that turns out."
The US President said: "The United States and the United Kingdom have done more good on this planet that any two nations in human history.
"That is thanks in large part to the traditions of British liberty which grew up on these islands." Mr Starmer hailed a "new era" for the special relationship between the country. He said: "This historic second state visit is a moment to celebrate the unique bond between our two countries.
"But today, we've gone far beyond that. We've renewed the special relationship for a new era. The United Kingdom, the United States stand together today as first partners on defence, first partners in trade - with the groundbreaking deal we struck in May - and now, with a new agreement that we've just signed this afternoon, we're confirming our status as the first partners in science and technology ready to define this century together just as we did the last."
Earlier Mr Trump said the UK and US partnership will get "stronger and stronger" as he and Sir Keir Starmer signed a new tech prosperity agreement. He told an audience of US business chiefs: "With this agreement, our cherished friendship with the United Kingdom is getting stronger and stronger.
"Again, I want to thank the Prime Minister. He worked very hard on this, in getting this deal done." The deal has been "long in the making", Trump said, adding it was a "real honour" to be sat alongside the Prime Minister.