Hi swordsy,
I'm afraid you really are jumping to conclusions on this one!
I know the water this 'carp' came from and it was most certainly never intentionally put in as part of any planned re-stocking programme. In fact the club concerned wouldn't even entertain the idea of introducing a known 'easy-catch' hybrid, whether it's F1, F2 - or even Formula Ford! This is a club water, NOT a 'pay as you poke' dolly hole stuffed full of fish. In any case we're anglers, NOT danglers!
Several of our members have fished this particular lake for more than 50 years without ever seeing a fish like this. You can call it what you like, but this is a one-off 'odd-un' which is nothing like the hard-fighting 'wildies' we are used to.
I was present when the fish was weighed and photographed. Just from its looks, my first impression was that it was a very old fish but that's only a gut feeling. Then again, I do have a large gut!
For what it's worth, I support the view that it could well be an illegal immigrant from someone's garden pond or aquarium, which was given an assisted passage into our lake when its 'caring' owner got fed up with feeding it.