Per Lawrence J in Birkley v Presgrave (1801) 1 East 220 at 228:
All loss which arises in consequence of extraordinary sacrifices made, or expense incurred, for the preservation of the ship and cargo comes within general average, and must be borne proportionably by all who are interested.
Per Blackburn J in Oppenheim v Fry (1863) 3 B & S 878 at 883:
I have a strong impression that, where a voluntary sacrifice is made for the benefit of the whole adventure, it is general average; whether the ship and cargo and freight belong to one only or to different adventures, or whether they are partially interested, as they might be in the case of a steamer, one in the hull and another in the machinery.
Milburn v Jamaica Fruit Importing Co  2 QB 540 at p.550 Vaughan Williams LJ said:
The liability to contribute in no sense results from the contract of carriage, but exists wholly independently of the contract of carriage, by virtue of the equitable doctrine of the Rhodian law, which as part of the law maritime has been incorporated in the municipal law of England.
St.Maximus Shipping Co.Ltd. v A.P. Moller-Maersk A/S  EWHC 1643 (Comm) at paras 39-41 per Hamblen J:
39. In The Jute Express Sheen J held (at p. 61 lhc-rhc) that: "Despite argument to the contrary, I have no doubt that the words "proper proportion" mean pro rata according to the values of the ship and cargo."
40. Maersk relied on this statement in support of its further or alternative case that the binding ascertainment in the Adjustment of the amount of General Average due from cargo does not extend to the ascertainment of the "proper proportions" i.e. to the valuations of the various interests involved in the maritime adventure. In this case that it is of critical importance on the facts as the assessment of the vessel’s contributory value includes added value based on the Adjuster’s determination of the sacrificial damage, the very matter in issue.
41. I agree, however, with the Owners that this serves to illustrate the implausibility of Maersk’s construction. It makes little sense for the parties to agree that the sum ascertained to be due in the Adjustment is payable whilst at the same time agreeing that constituent elements of the sum ascertained to be payable may be challenged. Valuation is an intrinsic part of the ascertainment which the parties have agreed to be binding. In my judgment the words "proper proportion" mean the pro-rated proportion, as Sheen J stated. They are descriptive rather than prescriptive words.