Bob,
Cranfield is a very busy place! I am obliged to fly close by there quite often, batting along quite quickly. Sometimes, such as yesterday, I find it extremely difficult to get a word in to announce my presence, especially when a single controller seems to covering more than one frequency and doing everything for everyone. It's made worse because the agency I really
need to talk to is Luton Radar because I usually need an airspace transit from them when going southbound. Thankfully, I fly with the luxury of a traffic avoidance system these days, which is a godsend as far as increasing situational awareness goes. Obviously, you don't have that luxury.
Rather than submit a report (an AIPROX would perhaps be more appropriate than a CHIRP), I would just learn a personal lesson from your experience and perhaps think about what you might do differently next time. For example, as you say, you could have descended earlier, or planned to fly further north. I would personally aim for at least 500 feet altitude separation if possible.
I note that you spotted the other aircraft first because he had a landing light on - there's something else to think about, .... your aircraft, in common with all light aircraft, presents a very small visual cue. A bright light can help increase your contrast. I often put on the landing/taxy lights in a busy traffic environment, especially if TCAS says something is ahead at a similar level but I haven't yet spotted it. I do often spot aircraft first (not saying I get 'em all) and notice that other aircraft do often use their lights to acknowledge they have also seen me.
Bear in mind that the airspace between EGTC and the CIT tends to be where the other (two) pilots' eyes will be inside more than is ideal. Even if it's an examiner and a candidate, the examiner will be watching how accurately his pilot is finding the beacon and flying the procedure. I avoid that airspace if possible, although in Class G anyone is at liberty to transit through it.
Yesterday I couldn't avoid it on the way from Luton and was therefore extra vigilant. I made sure I spoke to ATC as early as possible, made myself as conspicuous as possible, looked out as much as possible and included the TCAS in my scan.
Hopefully the other pilot will also be more vigilant in future and aim to increase his own situational awareness as a result of his part in your "encounter". He was in Class G after all and was also responsible for lookout, despite being on the procedure, even if declaring IFR (I take it you were both VMC, I know the Wx was quite good). He might have had IF screens up, which certainly wouldn't have helped him.
If he has submitted an AIRPROX report, you will get your say in the process and it isn't there to apportion blame. You saw him in Class G and took avoiding action. He saw you later and closer, possibly when he felt it was too late for him to resolve the situation and it startled him. Had you not turned, he might never have seen you, although you would have been closer to him. If it is reported, I would put money on it being classed as a category B or possibly a C, btw.
AIRPROXes are an emotive subject for most pilots. The last time I submitted an AIRPROX, some while back, it was because we saw another aircraft very late and had to take fairly energetic avoiding action to avoid a collision. The other pilot didn't appear to have seen me as he didn't take any avoiding action (as
he should have done iaw rules of the air). When asked by ATC he initially denied it could have been him at all (no doubt about that, I read off his registration as it went left to right, less than fifty metres ahead and only slightly above us, as he descended. Later he got very grumpy and declared in his report that he considered that it was up to other aircraft to be on his homebase "A/G" frequency nearly seven miles from that location, rather than the radar unit I was in contact with, and was to land at. ATC didn't see him on primary radar (although they saw us) and he wasn't using his transponder.
Take care.