... was also used by Anglican Catholics for purposes of survival under the tyranny of Henry VIII. The most famous example was the recognition by Henry VIII as Head of the Church by the Convocation of Canterbury. The assembled clergy signed up to the Government formula, but only with the addition of the words "as far as the law of Christ allows". They were 'mentally reserving' the proposition that Christ's law did not allow the royal headship at all.
Nowadays, the clergy of the C of E are not required as once they were to sware to use the Prayer Book "and none other"; they have to undertake to use only the forms "allowed by canon". This undertaking, of course, is easy peasy. On simply entertains a mental reservation that by 'canon' is meant the Code of Canon Law promulgated by Rome for the Latin Church in 1984. This, indeed, is the position demanded by our ecclesiology anyway. The same reservation modifies the sense of the the oath of canonical obedience to the diocesan bishop "in all things lawful and honest".
A possible additional Reservation when swearing the oath of canonical obedience would be that a See is in fact vacant; having been forfeited by heresy. Sedevacantism, indeed! It could be argued that when a bishop has deliberately and sacrilegiously purported to ordain women to the priesthood; has provided perhaps half of the parishes in his diocese with spurious ministers offering mere simulations of the sacraments; has flouted the authoritative teaching of the Roman Pontiff in Ordinatio sacerdotalis; has ignored the personal plea of a papal emissary not to go ahead with the 'consecration' of 'women bishops'; then he has been guilty of such contumacious, persistent, and unrepented heterodoxy embodied in heteropraxy that he must have forfeited his see. Personally I am not too sure about this. I am not a canonist, but surely, for us papalists, under the Code of 1984, it is necessary for the Sovereign Pontiff, by formal canonical procedings, to depose a bishop before his see becomes vacant. Naturally, Anglo-Catholics who do not take a fully consistent papalist position might not see it in quite this pedantic way, and might indeed feel that since there is no practical way of dealing with the rampant episcopal heresy in the modern C of E, one has to live with models of automatic forfeiture. But ... c'mon ... Johnny Barchester is a very nice man; mired in heresy though he may be, he is terribly sincere. Lean over backwards and grasp at any shred of an argument that, taking the rough with the smooth and considering everything in the round, he might still just possibly be the Bishop of Barchester. Give the bugger the benefit of the doubt. That's what I say.
But what, I hear you ask, about the Barmy Bishop of Bux?