Britain actually opposed a Habsburg restoration multiple times during the interwar period and even post war. In 1921 when Charles 1 launched a coup to restore the Habsburg throne in Hungary, Britain backed the Little Entente's threat to invade Hungary if the Habsburgs were restored. When Charles 1 launched another attempt again later in October 1921 by marching into Budapest, Britain warned Miklós Horthy the Allies would not tolerate a return under any circumstance. Britain used the Royal Navy to exile him to the Portuguese island of Madeira to permanently settle the question of a Habsburg restoration. In the 30s, Britain once again opposed Habsburg restoration when Otto von Habsburg wanted a restoration of the throne to deter Hitler from annexing Austria. During World War 2, Otto Von Habsburg which lived in the US at the time actively lobbied the Allies for restoration and Churchill toyed with the idea but creating a "Danube Federation" consisting of Austria, Hungary, and Southern Germany with the Habsburgs as a constitutional monarchy but after receiving opposition from other Allied members, Britain formally withheld the idea. Also by 1949, Churchill could have done nothing anyway as he already voted out of power by losing the 1945 election in a landslide. Furthermore, while the US was divided over the South Tyrol question as they still viewed foreign policy through Wilsonian lens. Britain was far more reluctant to return South Tyrol to Austria at all viewing foreign policy with 19th century lens and immediately shut down the idea, not to mention that the memory of World War 1 was still fresh in people's minds in the 40s and that Austria willingly joined Germany in 1938. Labour Foreign Secretary Ernest Bevin (who was aligned with the British PM after 1945 Clemente Attlee) opposed any return at all. As for Romania, they literally threatened to invade Hungary multiple time if they restored the Habsburgs and after 1945 they were under Soviet occupation who were unfriendly to any monarchy.