Thanks all. The crazy thing was, if you look at the picture, the conditions dont look at all bad. I've done that drive literally hundreds of times, almost daily - I'd have approached it the same 100/100.
I only had a service the other day - was told tyres are 7/7. Apparently that means perfect condition? - just as well really!
Without getting to scientificy.....all-season tires, in cold conditions become hard and give up lots of their fair-weather traction. Winter tires are made of a different rubber compound that stays soft and supple at sub-freezing temperatures. This allows them to retain their traction properties in cold weather.
And how does a winter tire without studs do well on ice?? Well, the answer is in the rubber compound. If you looked at it under a microscope, it would resemble swiss cheese (although, out of rubber, not cheese

). This, couple with the malleability of the rubber, allows air to get trapped in these 'sipes' as they are known. As the weight of the vehicle rolls the trapped air gets compressed, causing the air to get super-heated (a side-effect of compressing air really quickly) and it melts the top layer of the ice, thus giving the tires extra purchase. You can actually see the ice refreeze as the car rolls over it and passes by.
All-season tires are bad, bad, bad. Gives you a false sense of security. Summer tires far exceed dry and wet weather traction in 40degrees F + weather, and winter tires do the same 40 degrees F and below. They are a compromise. Remember, for all a cars fancy suspensions and brakes, they only utilize the only part of the car to make contact with the road. If you scrimp and save on things on your car, don't let the tires fall victim.