“… save in so far as Parliament has given guidance, it is initially for the commissioners to decide whether the underlying cause constitutes a reasonable excuse and for the tribunal to decide this on an appeal. That said, there must be limits to what could be regarded as a reasonable cause. Nolan LJ, as I read his judgment explaining and expanding on his judgment in Customs and Excise Commissioners v Salevon Ltd[1989] STC 907 , is saying that if the exercise of reasonable foresight and of due diligence and a proper regard for the fact that the tax would become due on a particular date would not have avoided the insufficiency of funds which led to the default, then the taxpayer may well have a reasonable excuse for non-payment, but that excuse will be exhausted by the date on which such foresight, diligence and regard would have overcome the insufficiency of funds.”