Is the principle of abuse of rights, as recognised in the judgment of the Court in Halifax as being applicable in the sphere of VAT, directly effective against an individual in the absence of a national measure, whether legislative or judicial, giving effect to that principle, in circumstances where, as here, the redefining of the pre-sale transactions and the purchaser sales transactions (collectively referred to as the appellants' transactions), as advocated by the Commissioners, would give rise to a liability on the part of the appellants to VAT, where such liability, on the proper application of the provisions of national legislation in force at the relevant time to the appellants' transactions, did not arise?