In reply to Mr Lopez:
You need insurance to drive on any land that the public could have access to. This includes closed roads like race tracks and open roads like supermarket car parks.
I think closing a road would be done by the police and it's not technically closing the road, it's the police directing you not to use it.
So the above example where other people are driving on the 'closed road' is because the police haven't directed them not to use it.
If you disobey a police direction then you're commiting an offence. That doesn't negate your insurance. It could be argued if you then had an accident, you contributed to it in some way by ignoring the sign so the pay out could be reduced.
It would depend; if you skidded off the road due to the snow, that might be contributory, if your car had a non snow related accident, that wouldn't be.
I guess it would have to be decided on a case by case basis.
Post edited at 18:20