This is despite claims from the industry that they have reduced their use by 82 percent in the drive to tackle antimicrobial resistance (AMR).

The British Poultry Council had claimed farmers had cut down their total use of antibiotics over the past six years from 81 tonnes to just over 14 tonnes annually. However BBC One’s Countryfile has discovered that figure does not include 281 tonnes of antibiotics known as ionophores, which AMR campaigners say pose a risk to human health and the environment.

Speaking within the programme, John Reed, Chairman of Antibiotic Stewardship with the British Poultry Council said that ionophores “are classed as feed additives” as they are not classed as antibiotics by the Veterinary Medicines Directorate. Although he conceded that whilst by definition it is an antibiotic, it is used only in animals and not in humans and he does not believe they pose a risk to the consumer.

Also speaking on the programme Cóilín Nunan, from the Alliance to Save our Antibiotics, said: “We are calling for ionophores to be made prescription-only but, really more fundamentally, we are calling for chickens to be kept in better conditions so that they don’t develop this terrible disease coccidiosis in the first place.”

High levels of ionophores, which are potentially toxic to humans, could leave residues in meat and in manure, which is used as fertilizer and could contribute to further spread in the environment. Campaigners fear certain ionophores could cause resistance to antibiotics that are medically important for humans.

The investigation is presented by Countryfile’s Tom Heap who speaks to chicken farmers across the UK, some of whom now farm completely antibiotic-free. Herefordshire farmer Richard Williams, who supplies meat to supermarkets and restaurants from more than one million chickens every year, told the programme he no longer used antibiotics to prevent illness.

He said: “Things have changed in the last five years – we’ve used antibiotics twice and that equates to about one-and-a-half per cent of the birds we produce here. From a farmer, a businessman, point of view, antibiotics cost money so if we can do without them it’s better for the birds, it’s better for me.”

Tom Heap concludes the investigation, saying: “The risk of using these drugs as an additive to chicken feed is clearly debatable. But the industry admits they are antibiotics and campaigners have told us that we can’t expect cheap chicken without them. So, consumers’ shopping decisions are down to your priorities.”

The full investigation can be seen on Countryfile on BBC One at 6pm on Sunday 31 March

This will be available to watch here