It is true that Law Merchant is sometimes spoken of as a fixed body of law forming part of the law, and, as it were, coeval with it, but as a matter of legal history this view is altogether incorrect… The Law Merchant is of comparatively recent origin; it is neither more or less than the usages of merchants and traders in the different departments of trade ratified by the decisions of the Courts of Law, which, upon such usages being proved before them, have adopted them as settled law with a view to the interests of trade and public convenience…

Per Chief Justice Cockburn in Goodwin v Robarts (1875) LR 10 Exch 337