Carp were brought into this country to eat, Via monks etc.
The main reason they are no longer eaten is the people who sport fish for them, angling clubs spend huge sums buying these fish, which can live for 50+ years, their investment is then payed back by selling tickets to catch em...If someone clonked a large carp and it became known, then there would be big repurcusions. #
Angling in Britain is very much about sustainability, we have many more people wanting to fish, than fish to go aound, hence the stocking of ponds with non native rainbow trout from fish farms. The weird thing is wild brown trout are far tastier, yet it is frowned upon to take, what is a very limited resource.
I have heard that zander,grayling, perch are good table fish, pike would be but for the bones, yet I will never try one due to the above comments.
I do catch and eat trout, and many sea fish, but interestingly the last fish I caught was a 5+lb mullet, and although I'd love to try mullet, I just couldn't kill such a stunning looking fish (prolly 15 years old) without need.
In a true survival situation you would, and should, have a go at most things, but it is very important when dealing with finite resources we tread lightly, and are seen to do so