I have always put a hyphen in the fragment "no-longer X", but neither the BBC website or the Economist seem to put one in. I always thought that
The piece of string was no longer than five inches.
should not have one, but
After I cut it, the string was no-longer whole.
needed one, because longer is a comparative. Certainly when I read the two sentences above aloud I put a different emphasis on the words.
Does anyone know if this is or was common? I'm from the UK, if that makes a difference to the answer.