Glynn v Margetson [1] is an English case on the law of carriage of goods by sea which established the "Main Purpose Rule" in relation to deviation.

A vessel, the Zena, was chartered to carry a perishable cargo of Seville oranges from Málaga to a marmalade factory in Liverpool.

Although a carrier has a duty to "proceed with reasonable despatch" [2] and not to deviate from the agreed course, the ship visited other ports in Spain and North Africa before heading for Liverpool.

Lord Herschell LC declared: ‘Where general words are used in a printed form which are obviously intended to apply, ...to a particular contract, ...

The Main Purpose Rule was subsequently adopted by the general English contract law in the 1956 case of Karsales v Wallis, recast as the "Fundamental Breach" doctrine.