Jeremy Bentham, Rationale of Judicial Evidence (1827), 7 The Works of Jeremy Bentham 473, 474, 475, 477, 479 (Bowring ed. 1842), as quoted in 8 John H. Wigmore, EVIDENCE IN TRIALS AT COMMON LAW §2291 at 549-550 (John T. MacNaughton rev., 1961):

When in consulting with a law adviser, attorney or advocate, a man has confessed his delinquency, or disclosed some fact which, if stated in court, might tend to operate in proof of it, such law adviser is not to be suffered to be examined as to any such point. The law adviser is neither to be compelled, nor so much as suffered, to betray the trust thus reposed in him. Not suffered? Why not? [1] Oh, because to betray a trust is treachery; and an act of treachery is an immoral act. . . .

[2] But if such confidence, when reposed, is permitted to be violated, and if this be known, (which, if such be the law, it will be), the consequence will be, that no such confidence will be reposed. Not reposed? — Well: and if it be not, wherein will consist the mischief? The man by the supposition is guilty; if not, by the supposition there is nothing to betray: let the law adviser say every thing he has heard, every thing he can have heard from his client, the client cannot have any thing to fear from it. That it will often happen that in the case supposed no such confidence will be reposed, is natural enough: the first thing the advocate or attorney will say to his client, will be, — Remember that, whatever you say to me, I shall be obliged to tell, if asked about it. What, then, will be the consequence? That a guilty person will not in general be able to derive quite so much assistance from his law adviser, in the way of concerting a false defence, as he may do at present. . . .

[474] If the law adviser, . . . the law neither commanding nor forbidding him, were to offer his testimony for the purpose of promoting the conviction of his client, the imputation of treachery would have, if not a good ground, at any rate a better, a more plausible ground. But the question is not, whether the lawyer shall thus offer his testimony; but whether the law shall command it, or authorize him, nay force him, to refuse it. . . .

[475] [3] "A counsel, solicitor, or attorney, cannot conduct the cause of his client" (it has been observed) "if he is not fully instructed in the circumstances attending it: but the client" (it is added) "could not give the instructions with safety, if the facts confided to his advocate were to be disclosed." Not with safety? So much the better. To what object is the whole system of penal law directed, if it be not that no man shall have it in his power to flatter himself with the hope of safety, in the event of his engaging in the commission of an act which the law, on account of its supposed mischievousness, has though fit to prohibit? The argument employed as a reason against the compelling such disclosure, is the very argument that pleads in favour of it. . . .