First the background. Although highly Teutonic, the Kingdom of Hanover was a territory under British sovereignty. In fact, the kings of Hanover were British royalty. See Monty Python sketches with Victoria speaking German. In any case, this is the British connection with Hanover.
Here are some excerpts from the article "Chief Rabbi Nathan Marcus Adler (1803-1890) Jewish Educator from Germany" by H. D. Schmidt in LBIY 7 (1962):
"In 1837 William IV died and the laws of Hanover did not permit Queen Victoria to become Queen of Hanover. The new King, Ernest Augustus, Duke of Cumberland, a son of King George III, abolished the liberal constitution and chased the protesting liberal professors out of the country. . .There you have it. In the fanciful account Victoria's son's right to the British crown might be contested "since he'd be considered a German citizen," but the fact was that Victoria's own right to the crown of Hanover was not allowed by Hanover's laws. In addition, we see that the influence of the Duke of Cambridge was crucial in tipping the scales heavily in R. Nathan Marcus Adler's favor. I guess Duke of Cambridge, ex-Viceroy of Hanover isn't nearly as dramatic as Queen Victoria. In any case, it's still puzzling to me that such a specific source (a printed lecture of the rabbi's son) is cited.
"In 1841 a letter reached Dr. Adler appealing for a contribution towards the relief of the Jews of Smyrna. The appeal was signed by Moses Montefiore. Dr. Adler sent twenty Pounds. It was the first point of contact between Dr. Adler and that nineteenth-century leader of Western Jewry. Despite the official connection between Hanover and Britain for so many years, Adler's personal contact with England was not wide. In 1842 London's chief rabbi passed away. After an "interregnum" of two years the Ashkenazi community declared the position vacant. A selection committee was formed among the honorary officers of the Ashkenazi synagogues. There was a dispute about the system of election as a result of which Birmingham, Bristol, and Newcastle Ashkenazi congregations declined to vote. The recently established reformed community of London had been placed under a cherem (ban) by the deceased Chief Rabbi and refused to have anything to do with that office, which had no place in the British Constitution, and which was, in their view, an obstacle to progress. Negotiations were long and tedious. Anglo-Jewry only numbered about twenty thousand people — mostly residing in London — but communal unity was not one of its virtues. Sephardi and Ashkenazi Jews lived their lives apart. The reform schism had made matters worse. Communal administration in which the state took no part, generated much heat and little efficiency. Most of the influence and the communal service came from a few wealthy families. The vote of the Rothschilds carried more weight than hundreds of less prominent names. In 1844 a short list of candidates was drawn up containing four rabbis, all from Northern Germany, Dr. Adler, Dr. Auerbach, Samson R. Hirsch, and H. Hirschfeld. Sir Barrow Ellis, the chairman of the Selection Committee, judiciously sounded the views of the other members of the Committee. They wanted a man who was a firm opponent of the reformers, yet no fanatic, inquisitorial, militant puritan. He had to fit into the British
climate of moderate conservatism. One decisive vote, however, was cast by a Gentile.
The Duke of Cambridge, ex-Viceroy of Hanover, thought he knew who was the right person the community wanted. In Britain important decisions are often arrived at over a cup of tea. So the Warden of the Great Synagogue, Baron Lionel de Rothschild, probably had tea with the Duke one fine day and the Duke convinced the Warden that Dr. Adler was the best choice. Out of the 134 votes cast, therefore, Dr. Adler received 121 and that settled the matter. Provincial Jewry was still very insignificant and Rothschild's views were not secret."
It is to be noted that over 5 years before my post Paul Shaviv debunked the story, and he did it without Wikipedia orArchive.org, although he does say that it took an entertaining hour with books and the internet.