The "crack" was on the starboard lower part of of nosecone. It started about halfway back and continued to the outside edge in a zig-zag pattern. Since we arrived safely at LHR I was obviously wrong about the crack but it would have been nice if the crewmember had taken a good look and not dismissed my concerns so lightly. Thinking about it afterwards I suspect he may have thought I was looking at the nosecone "strakes" and thinking they were cracks (I wasn't, what I saw was separate & different).