The first such relationships are those which are fiduciary per se, and secondly those which arise in the context of a relationship.3
In general the essence of a fiduciary per se - or status based - relationship is that one person occupies his position in which he has a duty to act on another's behalf and has the opportunity to abuse his position. Canadian law recognizes such a relationship existing between doctors and patients4 and even child-abuser and victim5. An unusual English example is that found in Reading v A-G  where a corrupt army sergeant accepted bribes from smugglers of drugs and spirits. He was held accountable to the crown for the proceeds of his crime. Asquith LJ defined the fiduciary per se relationship as follows:
(a) whenever the plaintiff entrusts to the defendant property and relies on the defendant to deal with such property for the benefit of the plaintiff or purposes authorised by him, and not otherwise, and (b) whenever the plaintiff entrusts to the defendant a job to be performedand relies on the defendant to procure for the plaintiff the best terms available6
Contextually fiduciary - or fact-based ...
However if one party makes use of confidential information derived from the negotiations to make a profit at the expense of the other it might do so.8 The law also recognizes the use of the fiduciary relationship as a means of achieving remedial justice. This was recognized as a third category by La Forest J in LAC Minerals Ltd v International Corona Resources Ltd :
In this sense the label fiduciary imposes no obligations, but is rather merely instrumental or facilitative in achieving what appears to be the appropriate result.9
Whilst no one argues with the correctness of the decision in Chase-Manhatten Bank NV v Israeli-British Bank (London) Ltd 10 the reasoning has been heavily criticised for artificial use of the fiduciary relationship in order to provide a remedy. The Plaintiff had mistakenly transferred $1m to the Defendant, who had since become bankrupt. Goulding J held that the Defendant had become a fiduciary of the Plaintiff and so held the money on a constructive trust. In this way the Plaintiff retained a proprietary interest to the value of $1m from the assets of the Defendant. This was necessary because the alternative would be a personal right to restitution at common law on the ground of mistake, which would be meaningless as the Defendant was insolvent.
In some cases the House of Lords has allowed the equitable remedy of account of profits for a claim for breach of contract11 where the common law remedy of damages would have been inadequate. The equitable remedy of account of profits is normally available where there is a fiduciary relationship but the House of Lords permitted its application in exceptional cases where it was the effective way to remedy a wrong.