You're showing your age there! Those ads must have been 40 years ago now.
As an added bonus, the orange glow would be a useful safety feature when dog walking in low light. Better than a high-vis jacket!
More seriously, insulation is better than heating since humans create a lot of heat. Reducing heat loss is more efficient than adding more heat to be lost, since the amount of heat that can be added has to be low enough to be safe. If you're in a "this will kill you quickly" temperature then maybe insulation plus heating would be worthwhile, but that's more extreme than you're likely to get in the UK.
The coldest temperature I've been in for an extended period of time was -18C.
Not including wind chill. -18C was the direct air temperature. The biggest issue was breathing. You damn well know when the air you're breathing is that cold. I didn't need any extra heating, though. I was suitably clothed. Hands and feet were the main things, but I had suitable gloves (inner and outer) and suitable socks (inner and outer) and footwear. Layers matter. Maybe you could be OK with a single layer of some very specialised material, but layers make a lot of difference even when the clothing is fairly ordinary. Today, for example, I was too hot and had to open a couple of layers. It was 0C and the wind was up enough to make it necessary to lean disconcertingly forward in order to stay upright, but I was overheating in my 3 layers. I walked a couple of hundred metres with both outer layers open and the wind howling at a thin polo shirt. That cooled me down pronto. My legs were freezing anyway because I only had 1 layer on them and it was thin cheap trousers. Layers are the key.
