Does Derksen "Bazooka" Wayne Tank?

The Wayne Tank principle concerns the issue of whether a policy responds when there are two proximate causes which give rise to a loss, when one of the proximate causes falls within the cover afforded by the policy and the other falls within an exclusion.

As Cairns LJ explained, the principle is as follows:

If one cause is within the words of the policy and the other comes within an exception in the policy, it must be taken that the loss cannot be recovered under the policy. The effect of an exception is to save the insurer from liability for a loss which but for the exception would be covered. The effect of the cover is not to impose on the insurer liability for something which is within the exception.