Having done more research, the waste transfer station at Red Lodge (used for BSE waste) falls within the radius of the BM mast. The site, which appears to be alongside car scrapyards looks (from Google Earth) to be very easily accessible to anyone. Now, what if, having gone elsewhere in BSE such as a party, something happened and he was taken with his phone to that waste transfer site and perhaps put in waste that was already there, having been processed, waiting to be taken to Milton landfill that morning? The site starts operating on Saturdays from 7.30am and the phone would go off the BM mast shortly after leaving the site, around 8am?
The original bin lorry going on its supposed route to BM roundabout would get into the BM mast range at around the same distance from the mast as would a car on the road that goes to Red Lodge. That scenario would explain the lack of forensic evidence of that bin lorry and would 'loosely correlate' with the route and time it took to get into the mast range. It would also explain why nothing was picked up in the processes the waste goes through.
ETA: Apologies for all the posts in a row.