As Neal says, nobody can do much to help without some names and dates.
Were his parents married when he was born. If not you should look for his birth in his mother's maiden name. Could his mother have been one of the many women who went out to India at that time to work, often for military families. That could explain a birth in Quetta which at that time was India, Partition was not until 1947.
Have you found his mother in all the appropriate Census prior to his birth.
As Ayashi has already told you, you can be born in different countries and still be British. My own family are all British but born in Malta, Gibraltar, Singapore,Hong Kong, Canada, Grenada and Africa to name but a few countries. It is the same with most military families.