The celebrity press has reported that Princess Beatrice will become an Italian countess upon her marriage to Edoardo Mapelli Mozzi. While it’s true that Mozzi is technically an Italian count, foreign titles of nobility have no legal status in the United Kingdom.
At one time, foreign titles could be used officially in the UK if the holder obtained a license from the Sovereign, but from 1893 onward, such grants were only supposed to be made in exceptional circumstances. World War I led Whitehall to take an even harder line. In 1920, King George V issued a royal warrant that revoked past royal licenses for titles granted by Austria and Germany. However, other licenses were allowed to remain in force, for the moment.
The Home Office finally revisited the issue in 1930. The impetus for the change appears to have been the formalization of the Pope’s rule over Vatican City following the Lateran Treaty of 1929. The British government had previously refused to officially recognize papal titles of nobility on the grounds that the Pope wasn’t a temporal sovereign, but that argument was no longer sustainable. Still, the idea of having to recognize papal titles was highly unpalatable, as there was fear that recognizing papal titles could lead to divided loyalties. In a 1930 memorandum, Home Office mandarin Arthur Eagleton wrote that “[f]ew British subjects are in a position to render any special service e.g., to the Kings of Italy or Spain, and fewer still are likely to be under any temptation to do so at the expense of their own country. But a conflict of interests between his Church and his country either in domestic or foreign politics is liable to arise at any time for a Roman Catholic in Great Britain.”
Even secular Italian titles were viewed with suspicion by the Home Office. In the same 1930 memorandum, Eagleton wrote “[i]t has to be remembered that Italy has for centuries past been a country where every land-owning family had or could easily acquire a title, and that people who in England would be merely country squires of quite minor importance are normally counts or marquises in Italy.”
“Naturally therefore an Italian Government –which is what the Vatican is on its temporal side–is not likely to appreciate the dignity and importance which attaches to the possession of a title of nobility in England or to observe English standards in granting titles for services rendered,” he continued.
While the official policy was that licenses to use foreign titles wouldn’t be granted, in practice, the rule had been bent with some regularity. Eagleton noted that 13 licenses had in fact been issued since the prohibition ostensibly came into force in 1893. But in his view, many of these license were granted to the ‘right’ sort of person: “[o]f the 10 grants since King Edward’s accession, nearly all the titles were of considerable antiquity, and the majority were cases of families of foreign extraction who had possessed the titles before settling in England. There was no doubt therefore of the respectability of the applicants or their titles.”
Eagleton proposed that it was finally time to close that loophole once and for all. “It is possible that a re-adjustment of the general practice may make it easier to deal with the difficult Question of Papal titles.” Consequently, he recommended that the grant of royal licenses should cease once and for all.
The matter was subsequently referred to the Palace, and on May 26, 1930, the King’s Private Secretary, Lord Stamfordham, informed the Home Office that the King had agreed that no further licenses should be granted. Existing licenses would be extinguished, though current license holders, their heirs, and their heirs’ heirs (provided they were already born) could continue to use their foreign titles.
The Home Office informed the current license holders of the change and allowed them to raise objections. A protracted correspondence with them ensued, but the necessary royal warrant was finally issued on April 27, 1932 (the warrant doesn’t appear to have been gazetted, but it can be found here). From that point onward, foreign titles would no longer receive official recognition in the UK.
Consequently, even though Princess Beatrice may become an Italian countess after her marriage, it’s unlikely she’ll use that title in an official manner.
 Memorandum by Arthur Eagleton dated April 3, 1930 in François Velde, “HO 45/25906,” Heraldica.org, https://www.heraldica.org/topics/britain/TNA/HO_45_25906.htm. Hereinafter cited as ‘Velde’.
 Lord Stamfordham to H.R. Boyd, May 26, 1930 in Velde.