It's not just chicken, it is still the case that vets, under pressure from farmers, use antibiotics prophylactically with other farm animals where less than ideal welfare standards are the norm.
There is some cooperation between the medical and veterinary professions to address overuse of antibiotics that goes back to a commission set up by David Cameron et al in 2014 or thereabouts I think. The EU and the UN have both expressed concern about this but its not difficult to find reports about the huge problems of antibiotics and the farming industry of the US. Sadly, this leads immediately to the dreaded Brexit and pressure on the UK to make trade deals that water down food standards and animal welfare.
This is all compounded by the insistence that food must be cheap. It's all very well for those of us who can afford to buy organic and who know how to budget and cook inexpensively but how we change the larger situation I do not know. There was a GN thread a while back, begun in all innocence about the average person no longer knowing how to do either which quickly deteriorated into a slanging match about some people not understanding the living conditions of the less well off. I find that unhelpful, sad and distracting.
I think Jamie Oliver was ultimately vilified for his healthy eating campaign which is a shame but perhaps the way forward is small scale iniatives and hoping that the government can be persuaded to act for the greater good and not just trade agreements.