Julian,
Because they are so very thin, and appear to be a 1 piece shell construction (fiberglass or carbon fiber) I think they are a racing seat that has been re-upholstered in leather. The question is "who's racing seat". Most racing seats have much higher bolsters in the hip and rib area.
These may be some older seats before the high bolsters became commonplace, or the shells may have been cut down on the sides for more comfort and easier ingress/egress, or these may be a brand I haven't been able to find on the internet.
However, they are similar to the Sparco Roadster, which has fairly low side bolsters from the factory, see pic below.
The good news is racing seats with fiberglass shells are relatively inexpensive.
cowboy from hell
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