I agree with corporate wage slave - I had the same situation two weeks ago. I had checked in for a LHR to STR flight, but was not issued a boarding pass, and had the same message about my passport needing to be checked. I arrived ~40min ahead of my flight, and went to the counters - initially they misunderstood the situation and told me check-in was closed, but when they realised I just needed a passport check they did that quickly and let me go on my way.