My town, which coincidentally happens to be Oxford like in the article, has its own local site "Daily info" which includes user-submitted restaurant reviews, and the review form asks you not to make allegations of food poisoning (presumably for legal reasons) and to submit possible food poisoning reports to the local authorities for investigation instead.
I note the Chinese takeaway I got food from last week shows up on this map as a bright red blob...
> Are you allowed to complain about food poisoning on Yelp?