LONDON—A British court on Tuesday ordered the ruler of Dubai to pay his ex-wife and their children close to 550 million pounds ($730 million), in one of the most expensive divorce settlements in British history. The High Court said Sheikh Mohammed bin Rashid Al Maktoum must pay 251.5 million pounds to his sixth wife, Princess Haya Bint Al Hussein, and make ongoing payments for their children Al Jalila, 14, and Zayed, 9, underpinned by a bank guarantee of 290 million pounds. The total amount the children receive could be more or less than 290 million pounds, depending on factors including how long they live and whether they reconcile with their father. The settlement includes 11 million pounds a year to cover security costs for Princess Haya and the children while they are minors. Judge Philip Moor said the family needed “water-tight security,” and that “absolutely uniquely,” the main threat to …