That's a lot of confidence for someone with Onley's results and after him somewhat cracking yesterday.
I don't think those odds really indicate much. Betting is popular in Britain, and many like to bet on their countrymen. This often results in lower odds on British riders.
But which insider knowledge would that be? Onley has been saving himself for this stage where he will crush everyone?It's 365 so although a lot of British traffic it's an international bookmaker, see: Adam Yates at 41.00 despite being a much more accomplished rider and all things being equal more likely to win on the given profile. It is sometimes just an outlier but silly odds like Onley's today can suggest insider knowledge, you'll get more of the nationalistic stuff in bigger races as not many casual betters paying much attention to the Dauphine on a working day.
Could also just be some Scottish gambling addict lumping on his life savings.