Except that all free trade deals are, in fact, symmetrical and a free trade deal is what the U.K. and US are negotiating.
Calling a turd a chocolate bar don't make it so. The UK won't get a veto on US trade deals, whereas the US will on future UK trade deals. Call it what you like, symmetrical, asymmetrical, or Gerald the friendly Gorilla. It still ain't a great day for the people of the UK.
There's also the rather convoluted way the US works. No matter what trade deal is agreed at a federal level, it doesn't place any obligations on any of the 50 states (or companies therein) to actually do business with the UK. So you won't find many (if any) UK companies bidding for - let alone winning - US state contracts. Whereas (naturally) US companies will continue to bid for (and expect to win, or they will sue) UK contracts at all levels.
But that's drifting away from mere food standards, which is what this thread was originally concerned with.
It's quite telling that currently we couldn't import any US chicken to give it a try, as it wouldn't be up to current regulations.