Surely it's basic airmanship not to fly across an instrument approach, especially if you know there's traffic on it. If you have to, then be somewhere the other guy isn't going to be, i.e higher or lower. If memory serves the base of controlled airspace around the CIT is FL55.
Secondly, if you are going east to west and he's coming down an instrument approach on r/w 21 then HE has right of way..... and doubly so since he's landing.
Don't bother with an airprox. Learn from it, have chat with Cranfield and even the jetstream crew (I can put you intouch with them if you like).