"In circumstances in which a taxpayer has had ample opportunity to make accurate returns but has failed to do so for reasons within their control we cannot see how it is possible to argue that the imposition of a statutory time limit gives rise to a result which is either unfair or disproportionate. To allow a taxpayer in the Appellant's position to make claims outside the statutory time limit would be to remove any force from the statutory time limits themselves, to the disadvantage of both HMRC and tax payers"