Right now in Suffolk, the answer is...
We pull the live air temperature, wind speed, cloud cover and solar radiation for your spot from Open-Meteo, then estimate how hot a dark tarmac pavement in direct sun is likely to be. Pavement can sit 20 to 30°C above air temperature on a sunny, still day, which is why a 25°C afternoon can feel grim underfoot for a dog.
The verdict combines both numbers against guidance from the RSPCA, the Royal Kennel Club and several UK vet practices.
This is an estimate, not a measurement. Local conditions vary, shaded grass is always cooler, and a light concrete path is kinder than dark asphalt. If in doubt, walk at dawn or dusk, or skip a walk altogether. No dog ever died from missing one.