Having winter for six months of the year I may have some experience in winter driving. First of all, ESP will not change the law of physics for you. It will help you in controlling the vehicle if skidding but if you go too fast into a bend the car will run off the road anyway.
Second, winter tires is the key to safe winter driving. Driving with summer tires in snowy/icy conditions should be (and is here) against the law. Until you have actually compared driving with good winter tires against summer tires you will not understand what I mean. The difference is just unbelievable.
Third, adjusting the speed to road conditions. This sentence says it all.
Now, for the A2's capabilities on snow and ice. I've been driving with 155/65-15 as winter tires. These are Continental Winter Viking tires with spikes in them, probably not allowed in the UK. Winter tires should be as narrow as possible to avoid sliding above slash instead of through it. The A2 with these tires performs well, and the light weight of the car is noticed when manuevering on slippery roads. The car stops fast and is quite neutral in keeping the rear end where it is supposed to be. The ESP is good for that purpose, but if it kicks in you are driving too fast or too aggressive for the road conditions, it's time to slow down. Invest in winter tires marked M&S for "Mud and Snow" and follow my recommendations above and you will hopefully be just fine during the winter.