With the approach of Summer even with moderate temperatures your dog can be at risk of overheating. Recently six dogs had to be rescued from vehicles at the Badminton Horse Trials as temperatures rose.
Last month the RSPCA conducted an experiment leaving a thermometer inside a van. With the ambient temperature at 15ºC within an hour the temperature inside the van had risen to 45ºC
Even if you don’t think its a warm day always remember to leave plenty of ventilation and try to find some shade when you leave your dog in the car and continually check on them