FFS
My own theory is that Jeremy trained on his exercise bike at Bourtree Cottage. He needed to get himself into shape, Jackie.
The man was driven and obsessed by the Tour de France and his chance at the Tour de Yorkshire, and eventually this ill-starred ambition and greed - a tragic warping of the more traditional values of amateurism and sportmanship instilled at Gresham - overtook his better judgement and he started taking steroids to enhance his performance. Over time, the training costs mounted - elite cycle instructors don't come cheap, and there's tour fees to think about - so he had to think of a plan to get his hands on some big money.
Now, it was well known around Goldhanger that after long days in the fields, Jeremy trained by night and that's why he borrowed June's bike, to take things a step further as demanded by his French instructor, Jean-Pierre, who told him that his exercise bike didn't cut it anymore.
This meant Jeremy had the perfect excuse if he was caught. As it happened, he was. A secret memo from the COLP investigation shows that on the very morning of the murders, Stan and Taff grilled Jeremy over bacon and sausages and asked him why he had been seen out in the dark riding June's bike along local footpaths at around the time of the murders. Jeremy patiently explained that he was an elite cyclist and this sort of arduous training was essential for his proposed cycling career, an endeavour that had the full knowledge and approval of Nevill.
Taff was certainly satisfied with this explanation, and Stan was too. The problem for Stan was the bacon. Stan had been studying sports science in his spare time and had read the considered works of some of the elite Continental sports nutritionalists, and he just couldn't reconcile why Jeremy, an elite cross-country cyclist, would want to risk his waistline in that way. The suspicion in Stan grew, and although he accepted Jeremy's reason for being out in the dark on his bike, the bacon really was a step too far.
Unfortunately, Stan stepped over the line when he changed his pocketbook to say that Jeremy had enjoyed his bacon with ketchup rather than HP sauce.
Anyway, yellow jersey to Adam.