The US and the UK recognise that Taiwan is part of China.  Yet they speak as if 

Taiwan’s independence might be endangered and Taiwan need their protection, military if need be.

The BBC gives the impression that Taiwan is under threat.  It is ambiguous, as at times it is very careful about stating that the Chinese planes flying near Taiwan are operating in international airspace.

However, what the BBC never say  is that the official UK position is that Taiwan is Chinese territory – see  https://publications.parliament.uk/pa/cm199900/cmselect/cmfaff/uc574iv/574m15.htm

UK POSITION  ON THE STATUS OF TAIWAN

  3.  HMG recognised the Government of the PRC in 1950. We retained a British Consulate in Tamsui outside Taipei, accredited to the provincial authorities of Taiwan, until 1972. At that time, an agreement was signed with the PRC allowing for an exchange of Ambassadors with China. The Consulate was withdrawn at that time and since then there has been no official UK representation in Taiwan. Under the terms of the 1972 agreement with China, HMG acknowledged the position of the government of the PRC that Taiwan was a province of the PRC and recognised the PRC Government as the sole legal Government of China. This remains the basis of our relations with Taiwan. We do not deal with the Taiwan authorities on a government to government basis, and we avoid any act which could be taken to imply recognition.

And the same is true of the US, as has been restated by the Biden administration – see State Department website at https://www.state.gov/u-s-relations-with-taiwan/ in a section entitled US relations with Taiwan:

The 1979 U.S.-P.R.C. Joint Communique switched diplomatic recognition from Taipei to Beijing. In the Joint Communique, the United States recognized the Government of the People’s Republic of China as the sole legal government of China, acknowledging the Chinese position that there is but one China and Taiwan is part of China. …

The United States does not support Taiwan independence.

Given that both the UK and the US regard Taiwan as Chinese territory, how can they assert that it would be contrary to international law for Chinese planes to fly through Taiwanese airspace (which it hasn’t done, at least not recently) or indeed to overfly Taiwan?  More fundamentally, how can there be such a thing as Taiwanese airspace, since Taiwan isn’t a state but is part of China?

Like the US and the UK, the official policy of Australia is that Taiwan is a province of the Peoples Republic of China:

“The Australian Government continued to recognise Taipei until the establishment of diplomatic relations with the PRC in 1972. Australia’s Joint Communiqué with the PRC recognised the Government of the PRC as China’s sole legal government, and acknowledged the position of the PRC that Taiwan was a province of the PRC. The terms of our Joint Communiqué dictate the fundamental basis of Australia’s one China policy – the Australian Government does not recognise the ROC as a sovereign state and does not regard the authorities in Taiwan as having the status of a national government.”

https://www.dfat.gov.au/geo/taiwan/australia-taiwan-relationship