London doesn't really do dramatic heat or dramatic cold for most of the year, which is exactly why the genuine exceptions — a proper heatwave, a hard frost — catch people out. The right response to either is almost never "skip the walk entirely," but the adjustment worth making is different in each direction.

Heat: the pavement test

The single most useful practical check, and a genuinely well-known one worth actually using rather than just knowing about: press the back of your hand flat on the pavement and hold it for five to seven seconds. If it's too hot for your hand to bear, it's too hot for paws, full stop. Time of day matters more than the day's forecast high in a temperate city like London — early morning or evening walks sidestep the worst of it even on a genuinely hot day, while midday on the same day might fail the pavement test easily.

Watch for excessive panting that doesn't settle, seeking shade repeatedly, or noticeable lethargy — any of those are a sign to head home and try again later rather than push through, particularly for flat-faced breeds, who handle heat considerably worse than most.

Cold: mostly fine, with real exceptions

Most healthy adult dogs handle a typical London winter without any special accommodation — a normal walk at a normal length, no different from any other season. The exceptions are worth knowing specifically: very young or elderly dogs, short-coated or small breeds, and anything already unwell benefit from a coat and a shorter walk in genuinely cold weather rather than the usual routine.

Two practical things worth doing that aren't about whether to walk at all: check paws for grit or salt residue after a winter walk and wipe them down, since it can irritate skin between the pads, and watch for repeated paw-lifting or reluctance to keep walking, which is a clearer signal than temperature alone.

What the actual answer usually is

Almost never a full skip — usually a shorter walk, a different time of day, or both. This is exactly the situation Hapoo's streak handling was built around: a shorter, adjusted walk on a genuinely extreme-weather day still counts as itself, and a day that gets skipped entirely because conditions were briefly bad doesn't erase the pattern built over every ordinary day around it.

The honest rule of thumb, both directions: adjust the walk to the weather, don't cancel the habit because of it. One extreme day, handled sensibly, changes almost nothing about the bigger picture.