The human, once close enough to be overheard, does not really seem to expect himself to be intelligible; it's a lot of 'Oh really's and 'You don't say!'s.  The cat likewise is not earnestly trying to communicate: "Yep, yes, gotcha, for sure - nnnnooooo keep looking this way, over here - yes right good."

"Good morning," Cam meows, "I actually speak cat, what are you playing at here?"

The cat double-takes.  " - What."

"I said I actually speak cat, what are you playing at."

"I don't know what you mean!  I'm just here having a friendly chat."

(In the distance behind the police officer, a nearly identical cat trots slinkily into an alleyway with a comparatively enormous fish.)

"I mean, if you're just meowing at him because it's amusing, far be it from me to stop you, but it did seem weird. - is that other cat also a talking cat, the one with the fish?"

"I don't know her."

"I see." How is the person in the weirdass uniform reacting to another party joining the meowing conversation.

Pretending he was never part of it in the first place!  He's flipped his visor down and is standing up quite straight with his back to the nearest wall.

"Do you and this fellow know each other?" Cam asks the cat.

"Not intimately."

"Huh. Anyway, I suppose I've confirmed that there are talking cats in London."

"Where?"  The cat rubs a bit against Cam's legs.

"Sorry, Londinium, I'm from an alternate universe where the same city has changed names."

". . . Oh?"

(The same cat, or a third extremely similar cat, disappears into the same alley with another massive fish.)

"...would you and any friends you care to invite like all-you-can-eat fish for the duration of a conversation off somewhere?"

"Yes."

"Can you direct me to a good place for that?"

"After you get the fish and I get my friends, sure."

Cam offers the cat a sardine. It's subtle from human height but the cat can tell it wasn't there a second ago.

- And it tastes like a real sardine and everything?

Tastes like it was a live sardine just a moment ago.

". . . Wait here."  The cat runs off into the fish alley and returns a minute later, heading in the other direction with a passing rub against Cam's legs and an "Okay this way."  Cam is led along a slightly circuitous route - it almost seems like the cat might be trying to make him lose his way but if so it's not enough to be effective even in an unfamiliar city - to a building with several shattered windows.  "There's a tailless door up ahead a little," they say, leaping up on a windowsill and ducking through a missing corner in the accompanying pane.  There is indeed a human-sized door a bit farther along.