I mailed them a while ago with this question. Response: "We have a milled worsted which is flannel in appearance but much harder wearing under the English & Town Classic section." Ref number series 9400.
I was expressly told that they do not. They do have a finish that is not too dissimilar from a worsted flannel. I have a charcoal herringbone in it by Deboise. I can't remember the book but want to say that it is less than 12 ounces. Good stuff IMHO.