They look similar to Minorcas with the white lobes, but different proportions with smaller lobes and a larger comb, so a Black Leghorn x Minorca?
I know Belper quite well. Have friends who live there, bought Silkolene oil and worked at LB Plastics in Heage for a while. Used to be Crich motorcycle breakers near there once as well.
Brahmas seem to be the most popular breed here, but I did call into a big breeders in the North once on the way back down from the Uk and they had one twin-combed La Fleche- "Ferme de Beaumont' is was. Not as big an enterprise as I expected, but did buy their only bottle of egg sanitiser.
What I would like here are some more TNN's, but there is a lot of confusion developed here and they try to pass off Cou-Nu as the same, which they certainly are not. I'm thinking they are going to be better for heat resistance in the increasingly hot Summers.