Well, at first I was thinking that bananas go bad fairly quickly, but I guess the sailing time from Spain to England isn't actually long enough for that to have been a problem for banana imports? On the other hand, given your "Britain was going through one of its rare phases of not being at war with anyone," maybe the answer was that it was normally at war with any countries that were both close enough to be able to send bananas to England before they rotted and also with a good banana-growing climate?