Per Bankes LJ in Rederi Aktiebolaget Transatlantic v La Compagnie Frangaise des Phosphates de L’Oceanie (1926) 26 Ll L Rep 253 at p. 254.
Having regard to the whole tenor of the charterparty I think that they are inserted for a set purpose and in order to prevent the operation of the ordinary rule that when once a vessel comes on demurrage the time she is detained is to be calculated by running days or calendar days, as opposed to charterparty days.
Per Lord Reid in Union of India v Compania Naviera Aeolus, S.A. (The Spalmatori)  2 Lloyd’s Rep. 175 at p.179:
The loss must fall on someone, and one would think business people who made the contract would regard it as reasonable that the man whose fault it is should pay for it. That seems to me to be the basis of the rule, "Once on demurrage, always on demurrage".