Lowry uses the phrase twice in his novel Ultramarine, when Dana is being told about cleaning the captain's coffee pot; "All Lombard Street To A Tahiti Orange2 (Pg. 56) and later when the crew are discussing the chances of the survival Norman's pigeon in the sea "Yes. All Lombard Street To A Tahiti Orange on that, mate' said the boatswain, as he started to roll a cigarette. 'I'm afraid he'll make a nice little bit of supper for one of them sharks, supper eh?'" (Pg 149).
The origins are “`It is Lombard Street to a China orange,' quoth Uncle Jack.” —Bulwer Lytton: The Caxtons (Dictionary of Phrase and Fable, E. Cobham Brewer, 1894), meaning very heavily weighted odds; Lombard-street signifying wealth and a China orange poverty. The phrase is used in the context of making a bet, either explicitly or implicitly. To stake the Bank of England against a common orange is to stake what is of untold value against a mere trifle.
However, Lowry uses another version of the phrase which he must have recalled from his reading of Ocean steamships a popular account of their construction, development, management and appliances by F. E. Chadwick, U.S.N., J. D. J. Kelley, U.S.N., Ridgely Hunt, U.S.N., John H. Gould, William H. Rideing, A. E. Seaton (1891); "Very creditable, sir ; very well done. You may secure, sir ? " Very well done it is, and when you remember this is the first drill and many of the hands are new, you may feel reasonably assured, should any ordinary fire break out, that it is all Lombard Street to a Tahiti orange it will be subdued most promptly." (Pg. 155).
A "Tahiti orange" is actually a Otaheite lime is considered an acidless, sweet form of the Rangpur lime. In many languages it is called Otaheite orange or Otaheite Rangpur. The tree is similar to the common Rangpur but less vigorous and hence dwarfed. It is almost thornless and the purple coloration on the new shoot growth is more intense. Likewise, the fruit is similar but somewhat smaller, more commonly necked, contains fewer normal seeds (often none), and is insipidly sweet from lack of acid. The Otaheite lime is thought to have originated in India as are many other varieties of the mandarin lime. The name is a misunderstanding. To Europe it arrived via Tahiti and Risso described it in Paris as a citrus from Otaite (Tahiti) in 1813. Its route from there on is unknown but it was first listed as a potted ornamental in a 1882 nursery catalog in California.