I hope he had a good excuse:
https://www.bbc.co.uk/news/uk-england-leeds-56291594
It's a lot safer than most other places people are expected to cycle?
ETA:
The cycle route between Paris and Rambouillet for the start of PBP:
https://goo.gl/maps/YSptqeMgwhxcSwYx9
I don't disagree, on one occasion I have considered cycling down the A329(M), when commuting and Windsor & Maidenhead and Bracknell Forest had not gritted before overnight snow and ice. After witnessing a car in the hospital fence at Heatherwood and sliding the front wheel on approach to a Bracknell roundabout I approached the off slip from the A329 where it become motorway as down hill into the next roundabout was not appealing. My conscience got the better of me and I took the exit rather than ride through the junction with the M4. Fortunately Wokingham Borough had been better with the forecast and had gritted the rest of my route.
I did once end up cycling down the M40 by mistake... 3am run combined with a propped open emergency access gate (the "authorised vehicles only" sign therefore invisible). Oh, and signage on approach suggested that this was the left turn onto the A40, which was only 150m away! (A329 Milton Common junction).
Less than a mile to the next exit, which turned out to be 1.5 miles of spur motorway to the A40. Riding on the A40 after that point felt less safe than the motorway, as I was now in a live 70 mph lane, rather than a hard shoulder. Functionally, it meant I was a bit more paranoid about my rear light.
Whether my heebie-jeebie-o-meter is correctly calibrated is the question. One of the two cyclists to die on the motorway network since 2015 died on the opposite carriageway on that very stretch of the M40. My main concern was whether any vehicles approaching from the rear would be police...