I don't know for sure about American English (which I think* prefers 'in-'), but in British English they're both acceptable.
When I worked for OUP they had a rule (which I think was arbitrary) that a question was 'en-' and an official commission was 'in-'. So your context would require 'en-'. But I've seen both.
Come to think of it, maybe its 'en-'; one or the other! I'm trying to recall the sound in an American voice, and all I can be sure of is that AmE puts the stress on the first syllable, with schwa in the second, whereas in BE it's /ıŋ'kwaıri:/ (sometimes with the triphthong /aıə/ in the stressed syllable).