Per Lord Abinger CB in Roux v Salvador (1836) 3 Bing. NC 266 at p.285-286:
It is, indeed, satisfactory to know, that however the laws of foreign states upon this subject may vary from each other, or from our own, they are all directed to the common object of making the contract of insurance a contract of indemnity, and nothing more. Upon that principle is founded the whole doctrine of abandonment in our law. The underwriter engages, that the object of the assurance shall arrive in safety at its destined termination. If, in the progress of the voyage, it becomes totally destroyed or annihilated, or if it be placed, by reason of the perils against which he insures, in such a position, that it is wholly out of the power of the assured or of the underwriter to procure its arrival, he is bound by the very letter of his contract to pay the sum insured. But there are intermediate cases — there may be a capture, which, though prima facie a total loss, may be followed by a recapture, which would revest the property in the assured. There may be a forcible detention which may speedily terminate, or may last so long as to end in the impossibility of bringing the ship or the goods to their destination. There may be some other peril which renders the ship unnavigable, without any reasonable hope of repair, or by which the goods are partly lost, or so damaged, that they are not worth the expense of bringing them, or what remains of them, to their destination. In all these or any similar cases, if a prudent man not insured, would decline any further expense in prosecuting an adventure, the termination of which will probably never be successfully accomplished, a party insured may, for his own benefit, as well as that of the underwriter, treat the case as one of a total loss, and demand the full sum insured. But if he elects to do this, as the thing insured, or a portion of it still exists, and is vested in him, the very principle of the indemnity requires that he should make a cession of all his right to the recovery of it, and that too, within a reasonable time after he receives the intelligence of the accident, that the underwriter may be entitled to all the benefit of what may still be of any value; and that he may, if he pleases, take measures, at his own cost, for realising or increasing that value.