If the UK lowers its food standards to accommodate the USA, it's no good saying "well, I'll just buy British, then" because there will be nothing to stop domestic producers following suit. Indeed, they'll probably have to in order to try and keep up with a flood of cheap imports.
And it's not just chickens. There are a swathe of problems, from chickens to beef to GM crops to overuse of pesticides (and use of ones the EU banned) to chlorine washing of salads and other food items.
But the joyous cherry on the cake is that the US is also pushing to remove or reduce information about food origin on packaging (they're not stupid - they know if it says "Made in USA" on it, many people won't touch it). If they succeed, we'll have no idea where stuff comes from.
