The Chinese Nationalists began a military occupation of Formosa and the Pescadores in 1945. However, these areas were under Japanese sovereignty until 1952.

Oral Answer: Joint Under-Secretary of State for Foreign Affairs (Mr. R. H. Turton)
Date: May 4, 1955
Subject: Far East (Formosa and the Pescadores)

The case of Formosa is different. The sovereignty was Japanese until 1952. The Japanese Treaty came into force, and at that time Formosa was being administered by the Chinese Nationalists, to whom it was entrusted in 1945, as a military occupation. In 1952 we did not recognise the Chinese Nationalists as representing the Chinese State. Therefore this military occupancy could not give them legal sovereignty nor, equally, could the Chinese People's Republic, which was not in occupation of Formosa, derive any rights from occupation of that territory.

That position has been made quite clear by the statement the Prime Minister made in the House on 4th February, which has been quoted by the hon. and learned Member. Therefore I shall not repeat it. In reply -- I quote the concluding passages of his statement -- he said: Formosa and the Pescadores are therefore, in the view of Her Majesty's Government, territory the de jure sovereignty over which is uncertain or undetermined." -- [OFFICIAL REPORT, 4th February, 1955; Vol. 536, c. 159.] . . . . the fact is that Formosa is not under Chinese sovereignty. That does not mean that the Chinese Nationalists have no right to be there. Their presence springs from their military occupancy in which they were placed by the Allied Powers in 1945, pending future arrangements.

[ source: HANSARD 1803 - 2005 / Commons Sitting, 04 May 1955   vol 540   cc1865-74 ]

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