A quick look on google tells me it is definitely deemed offensive, and while some of the results refer to a gypsy origin many do not. However that doesn't interest me so much as finding out if this piece of angling dialect went any further than Boreham, Essex.
Dave as you know I was dragged up in Dagenham, Essex. (Now London). The term half chat was a common term for those of mixed heritage.
Regarding the the fish carrasin. I have posted on here before that I have caught lots of them in France mainly from waters that drain into the Rhone as far south as the Camargue. They look to all intents and purposes a crucian except the colouring which is silver not golden as in a true crucian.
Their habits are different to as they came from trotting running water.
Also posted on here before that about 15 or so years ago I caught what I am adamant was a chub/bream hybrid from the Lincolnshire Ancholme.
I was catching chub on trotted bread at Snitterby Weir and then had this fish. Very strange looking with the look of both species. About 4lb.
Whether it was a bronze bream or a silver b ream I cannot say as both are in this river.