Crown Immunity. Canada (Attorney General) v. Thouin (SCC, 2017)
In Canada (Attorney General) v. Thouin (SCC, 2017) the Supreme Court of Canada sets out the basics of when crown immunity may be overriden by statute (here the federal Crown Liability and Protection Act interpreted in acordance with the federal Interpretation Act), in the context of a party's attempt to examine for discovery the non-party chief investigator of the Competition Bureau within an otherwise private civil action. In this specific statutory context, the court denied the party the right to examine as sought, with the following broad comments:
 Crown immunity is deeply entrenched in our law. The Court has held that to override this immunity, which originated in the common law, requires clear and unequivocal legislative language. Over the years, both Parliament and the provincial legislatures have gradually placed limits on this immunity in order to draw the legal position of the Crown and its servants closer to that of other Canadian litigants. This is true in, among other areas, that of civil liability. Ultimately, it is up to the courts to give meaning to legislative provisions that narrow the limits of the immunity and to determine its scope, where necessary.
A. Crown Immunity
 Crown immunity has evolved over time in English and Canadian legislation and case law. At common law, the Crown could in times past be sued in contract or on a proprietary claim (G. Morley, in K. Horsman and G. Morley, eds., Government Liability: Law and Practice (loose‑leaf), at p. 1‑40). However, it had “a number of prerogatives that rendered civil litigation against it very difficult” (ibid.). This was because the Crown was exempt from several obligations that applied to ordinary litigants, including the obligation to provide documentary or oral discovery (ibid.).
 Thus, because of its immunity, the Crown was historically exempt from the obligation to submit to discovery in proceedings in which it was a party. This was the case even though it could require the opposing party to be examined for discovery, and even where it was acting as plaintiff (Morley, at p. 1‑40; see also P. W. Hogg, P. J. Monahan and W. K. Wright, Liability of the Crown (4th ed. 2011), at p. 90). This particular immunity was recognized in Canadian court decisions that predated the statutory provisions on Crown liability. The Alberta Court of Appeal explained the immunity as follows in Canada Deposit Insurance Corp. v. Code (1988), 1988 ABCA 36 (CanLII), 49 D.L.R. (4th) 57:
In my view, the rule that the Crown and its agents are not subject to discovery does not arise from the assertion of a Crown prerogative but from an accident of history. Nevertheless, I am bound by precedent to require statutory authority, strictly construed, authorizing discovery of a Crown agent or officer. [p. 61] If this immunity meant that the Crown was not then required to submit to discovery in proceedings in which it was a party, it stands to reason that, at common law, the Crown was certainly not required to do so in proceedings in which it was not a party.
 That being said, there is a presumption that the common law remains unchanged absent a clear and unequivocal expression of legislative intent. In Lizotte v. Aviva Insurance Company of Canada, 2016 SCC 52 (CanLII),  2 S.C.R. 521, this Court summarized the case law on this point and noted “that it must be presumed that a legislature does not intend to change existing common law rules in the absence of a clear provision to that effect” (para. 56; see also Parry Sound (District) Social Services Administration Board v. O.P.S.E.U., Local 324, 2003 SCC 42 (CanLII),  2 S.C.R. 157, at para. 39; Slaight Communications Inc. v. Davidson, 1989 CanLII 92 (SCC),  1 S.C.R. 1038, at p. 1077; and R. Sullivan, Sullivan on the Construction of Statutes (6th ed. 2014), at pp. 504‑5).
 In this regard, s. 17 of the Interpretation Act now serves as a starting point in each case in which the Crown might have immunity. It reads as follows: “No enactment is binding on Her Majesty or affects Her Majesty or Her Majesty’s rights or prerogatives in any manner, except as mentioned or referred to in the enactment.” In short, unless the immunity is clearly lifted, the Crown continues to have it. In Friends of the Oldman River Society v. Canada (Minister of Transport), 1992 CanLII 110 (SCC),  1 S.C.R. 3, the Court recognized that s. 17 is indeed the starting point for the analysis regarding immunity and that, as a result, where there are no express words in an Act to the effect that the Act applies to the Crown, “it . . . remains to be decided whether the Crown is bound by necessary implication” (p. 50).
 In the past, language similar to the words “except as mentioned or referred to” in s. 17 had been used in s. 16 of the Interpretation Act, R.S.C. 1970, c. I‑23, which provided that no enactment could bind the Crown, “except only as therein mentioned or referred to”. In Oldman River and in Alberta Government Telephones v. Canada (Canadian Radio‑television and Telecommunications Commission), 1989 CanLII 78 (SCC),  2 S.C.R. 225, the Court interpreted this wording and concluded that a legislature must use express language to lift Crown immunity unless it can be inferred that the purpose of the Act would be wholly frustrated if the Crown were not bound (see also H. Brun, G. Tremblay and E. Brouillet, Droit constitutionnel (6th ed. 2014), at para. IX. 90).
 With these principles in mind, it must therefore be determined whether, in the instant case, Parliament has lifted the common law Crown immunity from discovery and, if so, to what extent.
B. Limits on the Crown’s Immunity From Discovery
 In about 1950, Parliament, drawing on the Crown Proceedings Act, 1947 (U.K.), 10 & 11 Geo. 6, c. 44, that had been enacted in the United Kingdom, began to impose limits on the scope of the common law Crown immunity. In 1953, it passed the Crown Liability Act, S.C. 1952‑53, c. 30 (Morley, at p. 1‑41; Hogg, Monahan and Wright, at p. 9), which had the effect of expanding Crown liability and thus bringing the Crown’s legal position closer to that of ordinary litigants. That Crown Liability Act was the predecessor of the CLPA that is at issue in this appeal. Today, Crown immunity still exists at the federal level in the context of civil proceedings, but only within the limits set in the CLPA and the Federal Courts Act, R.S.C. 1985, c.F‑7, the scope of which Parliament remains free to change (Brun, Tremblay and Brouillet, at paras. IX. 72 to IX. 73). It follows that the Crown is not in exactly the same legal position as ordinary litigants, since it still retains certain residual privileges and immunities under the current legislation.