Holiday insurance to cover holiday cancellations from volcanic eruptions?

Whilst airlines may (or may not!) refund flight costs if cancelled due to the volcanic ash problems, is there any "top up" insurance policy to cover costs for my accommodation and car hire that I paid separately if we can't actually get to Spain? The web sites tell us about what happens to people stranded on holiday but what about those who cannot get there? Our holiday insurance company tells us that it is for the airlines to pay but the airline is vague about this. Can anyone advise?