After having missed 12 months, he’s taking no chances with Rose on 21st century Earth; he’s not keen on another slap. He convinces Rose to stay behind in the TARDIS momentarily while he checks things out. He’s stunned she actually complies.
Harriet Jones seems to have long since passed the height of her leadership, which means they’ve arrived late. Again.
“It’s you,” Harriet breathes. “I mean, you you. You’ve changed back.”
He doesn’t apologise as he retreats. He’s not that kind of man. He wonders whether he will be in the far-too-near future when Harriet apparently meets a different Doctor.