To be fair the following policy is quoted on the
National Rail site:
So you wouldn't be left without a ticket, but still would be greatly inconvenienced.
Admittedly it is harder to find the cyclist who has left their bike in a reserved space and gone to sit down, than the cyclist with a reservation who has been forced to prop their bike up in a gangway, but in my case the TM had the discussion with me just as we left Didcot, and stood with me all the way to Swindon to make sure I got off, making absolutely no attempt to even find the other person who's bike it was in the 20 or so minutes between. That is inexcusable in my opinion.