I've touched on this topic already, but this is a bit more detailed.
One technique I have when looking at this case is to think about difficulties and problems in reverse. An example is Sheila being found forensically 'clean', which is said to be incriminating for Jeremy; but when you really think about it, actually it potentially points more to Sheila.
Here we will discuss the phone calls. They are said to be a problem for Jeremy, but are they? The essential problem here for the prosecution is that just as the phone calls tie down Jeremy, they also tie down the prosecution. This is because if, as a hypothetical exercise, we assume that Jeremy is guilty, then the phone calls are related to Jeremy's movements that night.
Even if Jeremy planned all this, he didn't plan for Nevill to end up in the kitchen. This is probably why he made the telephone calls, but even if he intended to make the calls anyway, it's still very risky and looks suspicious because he has to carry out the massacre under time-sensitive conditions.
What do I mean by 'time-sensitive' conditions?
I mean:
(i). Let's remember that Jeremy needs to fake the call from White House Farm to Goldhanger.
(i). He then needs to make his own call to the police from Goldhanger.
(iii). He doesn't know if the authorities and the phone company can log calls in some way. If they can, then it looks suspicious.
(iv). This means he has maybe a 30 minute window, at most - at the very most - between completing the deed and making a call to the police, and even then it looks suspicious. Anybody with a half-a-brain will ask: Why the 30 minute gap? This problem becomes all the more acute if, as I suspect, the phone calls were the result of the incident going wrong, because he is then thinking on the hoof - quite literally, if my belief is right that he had to go on foot.
As it turned out, there really was a 'suspicious' gap between Nevill's call and Jeremy alerting the authorities, which is what you would expect if Jeremy is guilty, because he has to move from one location to another. The gap reported by Jeremy was something like 20/25 minutes, I believe.
It also turned out that the authorities/phone company couldn't log calls, but Jeremy wasn't to know this. He's not a telecoms engineer and it would be risky for him to research the point, as he is then creating a paper trail and/or witness evidence. For instance, if he asks at the local library or rings up the phone company, could somebody remember that enquiry months later and link it to him?
In fact, Jeremy's presumed lack of knowledge about civilian call logging is, in itself, a glaring flaw in the prosecution. Quite simply, how does Jeremy know that the police can't find out when and where calls are made? How does anybody know this in 1985? Just because billing wasn't itemised then, it doesn't mean the authorities and/or the phone company don't have the capability to track calls made.
The main point of all this is that guilters need Jeremy to be able to move to and from the farmhouse in quick order. They know he needs to be seen returning to Goldhanger, so that places him in Goldhanger. Whether he really is seen there is beside the point. It's dark anyway, but Jeremy won't risk not being there. They also know that Jeremy can't do this by car or motorcycle/moped/scooter. That's why they're keen on June's bike. Otherwise, the only way he can do this is on foot.
And I think on foot is the only reasonable possibility. It's simple and much, much less risky than by push bike. If on the way back he is caught, on foot, in the environs of Bourtree Cottage, he could - at a pinch - make some excuse about being out of the house because he heard an intruder or something like that. If he is caught with a push bike, he is done for.
The question is: If we give the prosecution the benefit of the doubt and say the gap is 30 minutes, could Jeremy have moved on foot within a time window of 30 minutes, so that he could get back to Goldhanger to place the second call? Take into account that he would probably need to change and shower and dispose of clothes, etc., before he makes the call, in order to remove forensic traces, so he would have less than 30 minutes to actually cover the distance.
As the crow flies, it's 2 miles. Allow more than that for having to perambulate over fields, streams and ditches, and circumvent populated locations and various obstacles, natural and man-made. He's a fit young 24 year old man, and he knows the land, so he can walk over fields and climb over fences, etc., without needing a torch. In theory, he could do it, but it would be hard.