The evidence that inspectors were on duty on the roads to see if drivers had correct permits shows, of course, that the State was administering the Act. But such evidence no more proves that Mason paid under compulsion than does the evidence of the issuing of permits and the collection of fees for them. Presumably all the carriers knew that the Act was not a dead letter. If it matters that Mason was told by his predecessor in business about s. 47 (2), that he saw inspectors on the roads and had his permit checked, the result might be to put the plaintiffs in a better position to recover back the payments which Mason made for permits, than a carrier who had not had s. 47 (2) brought to his notice, or had never met an inspector on the roads. But would not that be a strange result? All carriers, as I have said, must be taken to have known that the State was administering the Act. If the fact that the State was doing so proves that it was exacting money by duress, then no carrier could be held to have paid voluntarily. Obviously that would be too large an assumption to make. I think that it would be giving a false character to s. 47 (2) or to any other sanctions provided by the Act and to the mere fact that the Act was being administered, to say that these things constituted a threat or an intimidatory announcement. The material question is whether any officer of the defendant threatened to use the powers in s. 47 (2) against Mason if he did not obtain permits. There is no evidence that any officer ever made a threat to Mason to compel him to pay for a permit. Of course, if there were, it would be reasonable to conclude that thereafter Mason did not make any payment for a permit voluntarily. Proof that any other carrier's vehicle was stopped because its owner had no permit and that he thereafter paid involuntarily for a permit (if he did), does not prove that Mason (who had never had his vehicle seized or threatened with seizure) did not always pay voluntarily. Where a person complies with the law you cannot presume that he does so in fear of the possible consequences of disobeying it. Voluntary obedience to a law is compatible with knowledge that it contains drastic means of dealing with disobedience. All Mason's overt acts, except possibly his protests, tend to show that he voluntarily paid the sums of money expended on permits. I have stated my view as to the insufficiency of the protests as proof of compulsion. The protests are evidence of dissatisfaction, no doubt, but that is not enough. The inter-State carriers as a body decided in advance to pay under protest, and Mason was merely following that policy. There is no evidence that any officer constrained Mason by any action or threat of action to pay for any permit, and that in order to secure the use of the motor vehicle Mason obtained a permit and protested in order to show that the transaction was not closed and that he reserved his rights to rip up the transaction and recover back what he paid. Mason knew before he embarked on the business of carrying goods between Victoria and New South Wales that it involved, as the law then stood, paying for permits. If he was not willing to pay for permits it was open to him to sue for an injunction quia timet to restrain the defendant from seizing his motor vehicle in the event of his not obtaining permits: see Cam & Sons Pty. Ltd. v. Chief Secretary of New South Wales [1] . The evidence does not prove that Mason was constrained by any action or threat of action to apply for the permits. The reasonable inference, as I have already said, is that payment was his own free choice. The plaintiffs had profitable orders or contracts for the carriage of goods to execute. They must be taken to have regarded the fees to be paid for permits as a normal expense of the business. Accordingly, they arranged to cover the fees as far as possible by the price they charged. They paid the charges for fees under business necessity to enable them to proceed with their orders and contracts for the carriage of goods inter-State. It is not a reasonable conclusion that having arranged to obtain from their customers money with which to pay for permits they were coerced into applying it to pay for permits. In my opinion, there is no evidence which satisfies me that Mason paid any of these sums of money under duress or compulsion of any kind. There is no evidence that he was subjected to any such constraint or pressure, and that in order to enable the inter-State carrying business to be carried on without interference his only reasonable alternative was to pay and to protest against payment in order to save the plaintiffs' rights. Upon the sum of the evidence the circumstances are comparable with those in Werrin's Case [1] . The plaintiff in that case alleged that he was compelled by pressure and duress to pay an amount of sales tax on second-hand goods. He brought the action in consequence of a decision of this Court that second-hand goods were not within the scope of the Sales Tax Acts as they then stood. The case stated found that the Commissioner of Taxation had written to the plaintiff informing him that the amount of tax in question was payable under the Sales Tax Acts and that it "must be paid". According to that case stated the plaintiff there paid with reluctance. In that case there was an express demand to pay sent with the apparent force of the Acts behind it and the plaintiff paid with reluctance. In the present case, however, there is no evidence of any express demand to pay any amount sued for; on the contrary, payment is shown to have been made on the initiative of Mason, albeit under protest. In Werrin's Case [1] Latham C.J. and I were of the opinion that the facts were not sufficient to prove that the amount of sales tax was not paid voluntarily. In my opinion the reasons for that opinion apply here, for in my view, despite all the detail in Mason's evidence, it proves only that the sums of money in question were collected by the defendant upon the supposed authority of a statute when actually, according to the subsequent decision of the Privy Council, no authority existed. I think it is appropriate to quote here a passage from the judgment of Skerrett C.J. in Julian v. Auckland Corporation [2] : "I decide it upon the simple proposition, which appears to be well established, that where money is paid at a time when the law is in favour of the payee it cannot be recovered by reason of a subsequent judicial decision reversing the former understanding of the law: see Henderson v. Folkestone Waterworks Co. [1] " [2] . A statement of Gibbs J. in Brisbane v. Dacres [3] is important and relevant here: "We must take this payment to have been made under a demand of right, and I think that where a man demands money of another as a matter of right, and that other, with a full knowledge of the facts upon which the demand is founded, has paid a sum, he never can recover back the sum he has so voluntarily paid. It may be, that upon a further view he may form a different opinion of the law, and it may be, his subsequent opinion may be the correct one. If we were to hold otherwise, I think many inconveniences may arise; there are many doubtful questions of law: when they arise, the defendant has an option, either to litigate the question, or to submit to the demand, and pay the money. I think, that by submitting to the demand, he that pays the money gives it to the person to whom he pays it, and makes it his, and closes the transaction between them. He who receives it has a right to consider it as his without dispute: he spends it in confidence that it is his; and it would be most mischievous and unjust, if he who has acquiesced in the right by such voluntary payment, should be at liberty, at any time within the statute of limitations, to rip up the matter, and recover back the money. He who received it is not in the same condition: he has spent it in the confidence it was his, and perhaps has no means of repayment" [4] . There is no satisfactory evidence that any of the sums was paid under any duress, express or implied. It is therefore not established that the defendant received any of these amounts to the use of the plaintiffs. I would dismiss the action.