Praise be to Allah.
A woman is obliged to cover her face in front of non-mahram men according to the more correct of the two scholarly opinions, because of evidence which has been explained in the answer to question no. 11774.
It is permissible to uncover the face in some situations where it is required by necessity or need or interest, such as establishing identity, medical treatment, testimony before a judge, and so on. Please see the answer to question no. 2198.
But you should understand that necessity should be properly estimated and not exaggerated and you should limit it only to that which will meet the need. So if you have to uncover your face in order to prove your identity, then that should be limited to the face only, and you should also avoid adornment and makeup. If it is possible for a woman to establish your identity, then it is not permissible to uncover it in front of a man. You should ask for that at the British Council and in the airport, before you uncover your face.
If a woman cannot do that, then it is permissible to uncover your face in front of a man, and there is no sin on you in sha Allaah.
We ask Allaah to help and guide you.
And Allaah knows best.