The phrase "the only expert" is grammatically correct and can be used in written English.
Example: "John was the only expert on ancient Roman history in the entire department."
He is not the only expert espousing such views.
They seemed to believe Brexiteer MP Gisela Stuart: "the only expert that matters" is the voter.
"The only expert thing I know about a relationship is that I don't know anything.
A group of hikers stumbled on the rock art eight years ago, but Mr. Tacon is the only expert to have seen it so far.
Eddie Hayes, a prominent Manhattan defense lawyer, was the only expert interviewed yesterday who said he thought Detective Vasquez should tell his story to the grand jury.
Then we put a camera in their hands and say, "Hey, we're experts at making and teaching film, but you're the only expert in your story".
He said the striking workers were "not the only experts" who could run the equipment.
But surgeons are not the only experts who ought to be consulted.
It may also have the interesting effect of bringing American courts closer to those in some European countries, where the only experts are those appointed by the court.
What has since become clear is that Joffe, Dodge and Tripp were not the only experts to be left out in the cold.
After 35 years as a public school teacher, I can say that the only "experts" never consulted about the school system's problems are teachers.
