Mike - I know of no cases. I did a quick search on my legal databases and can't find any.
As far as private property is concerned, the position is covered by the Occupiers Liability Act 1957 where the occupier has a duty to keep his property safe for visitors. However the duty is no more than to "take such care as in all the circumstances of the case is reasonable to see that the visitor will be reasonably safe in using the premises for the purposes for which he is invited or permitted by the occupier to be there". It is akin to the standard imposed by ordinary negligence in that it is a duty to take reasonable steps.
However, if you cleared your path and made it WORSE - ie you used boiling water which then froze, you could be liable. On the other hand, if you knew that your path was extremely slippery and failed to clear it that could equally lead to liability.
As far as highway authorities are concerned, I did find one case where a chap was killed on an untreated road. The Court found that the duty of the Highways Authority only extended so far as to keeping the road in good repair and it did not extend to gritting it. I have found a couple of slip and trip where there is dicta to suggest that the Council have a duty to grit, however, the Claimants there have been unsuccessful given there has been a short period of time between the ice forming and an accident and also in terms of the Council's policy to allocate resources where most needed (ie to main roads). That is not to say there won't be others, I just haven't had time to look.