Especially as 20 miles is about half a gallon - or £2.
and one would hope that wear and tear on the Civic doesn't equate to £1 per 10 miles... (although, actually... I guess it probably does
)
However, whilst £4 is £4 is £4, and lots of little £4s do add up...
You would rather hope that the dealership would be willing to invest £4s worth of goodwill into the relationship
(but yes, if it's warrenty work, they should be able to get this back from Honda)