First of all take the letter or whatever to the dealer and show them, do not part company with it. If they copy it make sure you get the original back.
If that fails make a copy of whatever you have that says you have a four year warranty from the date of purchase. Attach a letter stating that you have a document, copy attached, that confirms that you have a four year warranty.
Send it, via recorded delivery to the Chief Executive Officer of the dealership with a copy to Honda's head office, you can track and trace the letter to confirm receipt.
Insist on a written reply whatever their decision and if in your favour keep it. If they still insist that you do not have a four year warranty go to your local Citizens Advice Bureau.
I suggest that the small claims court will not be interested because, as yet, you are not financially out of pocket.
Vic.