EX54 XVL is a Subaru Impreza used by HEMS doctors in London when they are not in their helicopter. It is a slight departure from their previous vehicles as the bodywork is bright blue rather than dark blue (see below). It still has the blue and green flashing lights and distinctive livery.
The side view of the same Impreza. The doctors and paramedics that are part of the Helicopter Emergency Medical Service are easily recognised by their orange jumpsuits. The website shown along the door sills is for a medical supplies company that sponsor them.