I again took the bike to work. I went for a steady 20 mile ride around inland Norfolk.
I was quite happy with the 18 mph average, especially as it was quite windy. It was interesting that the HR went to 177 at the start of the ride. Unlike recent high HR max readings, this was not a spike but a slow rise to 177 and slow recovery. I don’t think I noticed this at the time because I was following navigation on the Garmin. I suspect that this is nothing sinister and due to the strong wind being directly ahead at this point.