Well, it is a legal requirement if we have a cold spell and you are involved in an accident. You would automatically be apportioned part of the blame and fined, even if you were otherwise acting correctly. Also, you could be fined if you were to hinder the flow of traffic through lack of wheel grip, especially if emergency services are not able to get through as a result. On the other hand, you can simply hope that the weather holds or neither of the two situations described occur. Your guess of the likelihood of a worst case scenario like that happening is as good as mine. I only mention this because some people prefer to err on the side of caution while others are prepared to take the odd risk. I must admit, I'd count myself in the latter, although I like to be able to make some sort of rough judgment of what my chances are.