Question to the Home Office:

To ask His Majesty's Government whether they have a record of any head of a state that is a close ally of the UK being subjected to questioning by Border Force when transiting through a UK airport.

Border Force does not hold the data in an easily accessible format on Heads of State being subject to questioning.

There is specific guidance on the way Border Force handle government travel available on GOV.UK: https://www.gov.uk/government/publications/exempt-exm/exempt-exm