This is genuinely harder to judge by eye than it sounds, because "what a healthy dog looks like" varies enormously by breed. A number on a scale means very little without knowing what that specific dog's frame is actually built for. A vet's proper assessment is the real answer here; what follows is general awareness that helps frame that conversation, not a replacement for it.

The rib-and-waist check

A commonly taught, genuinely useful home check, generally known as body condition scoring in more formal terms: you should be able to feel your dog's ribs fairly easily without pressing hard, and see or feel a visible waist (a tuck-in behind the ribs) both from above, looking down at the dog's back, and from the side. No easily felt ribs at all usually points one way; ribs and spine both very prominent with no covering usually points the other. This isn't a replacement for a vet's actual assessment, but it's a far more useful home check than weight in kilos alone, precisely because it adjusts for the dog's own frame automatically.

"He just has a big frame" is sometimes true, and sometimes a story

Breed size genuinely varies enough that comparing one dog's weight number to another's tells you very little. The rib-and-waist check cuts through that confusion in a way a number on a scale can't, which is exactly why it's worth learning to do rather than defaulting to a number that was never really specific to your dog's actual build.

The London-specific pattern worth naming honestly

Pavement treats, a bite of something at a dog-friendly cafe, and well-meaning strangers feeding a friendly dog mid-walk all add up in a way that's genuinely easy not to track. None of it feels like "feeding" in the moment, and all of it counts the same as anything measured out at home. Worth being honestly aware of, especially for a dog that spends a lot of time out and about meeting people.

Why this is a trend question, not a single-meal one

Weight tends to shift slowly, over weeks and months, rather than as the result of any single day, which is exactly why a single indulgent afternoon isn't the thing to worry about, and a consistent pattern is. This is also why a steady daily walking habit, rather than one occasional long effort, is the thing that actually helps over time: small, regular walks that reliably keep happening do more for a trend than one big correction ever does.

If there's real uncertainty after an honest rib-and-waist check, that's exactly the kind of specific, quick question worth taking to a vet rather than sitting with. It's a genuinely common question, and a fast one for a professional to actually answer.