It is a very grey area with assistance dogs as I had similar at another event but not speedway. They told me I had to produce a certificate but is not such a thing as a registered certificate in the uk unless it is given to you by the occupational therapist or from social services.
Think this has been on the cards for at least 6-7 years and now it has happened I wish them good luck.Hope they can get something sorted but think it will be at least a minimum year off.