Your insurer is obliged to pay out under the statutory third party cover irrespective of any factors such as the weather.
However insurers can, and do, refuse to pay out on additional cover (such as fire,theft and comprehensive cover) where the driver has failed to use due diligence. So, for example, an insurer would almost certainly fail to pay out for the theft of your vehicle if you left it with the keys in the ignition.
Similarly an insurer would probably refuse to pay out if you wrecked your vehicle after driving past a sign saying 'Road Closed Due to Snow'. They might also refuse to pay out (beyond the statutory 3rd party element) in other circumstances where a driver should have known that it was unsafe to drive. So, for example, if you drive into a flood when there have been clear warnings on TV and radio about flooded roads in that area, you might have great difficulty in getting any money from your insurer.
Chris