We have a problem with configurable products and UK VAT, we need to be able to apply 0% tax on children sizes and the standard 20% tax on adult sizes but configurable products do not respect the tax class id set on the simple products used.

I checked out the BCP module but that does not handle this unfortunately. 

I think a custom module is required that bypasses the configurable products tax class and instead grabs the tax class id of the simple product that has been selected.

Having not had to deal with Magento core very much I have tried to find a way to over-ride the tax class id used but so far no luck, would some body be able to point me in the right direction or better still if I've missed another solution to this?