I went back and caught another five the next day and they really vary from a crucian with barbels to a text book common. Pics in the next reply.
Most probably...nature making her adaptions...but in some established pools only a fraction of carp are feral like... it's puzzling
I had a nice feral today that looked chub like. It came from a tiny tidal river with some big chub in it. In this case I'd say it was convergent evolution.