The investors asked the companies in the US and UK to produce a comprehensive strategy for dealing with the issue, and set out clear timelines for reducing antibiotic use.

In a statement, the group 'Farm Animal Investment Risk and Return' said: "The investors are concerned that a failure to confront irresponsible antibiotic use poses significant risks to their investments.

"These include the substantial risk of regulation as antibiotic overuse has increasingly become a target for stricter regulation in both the EU and US; further regulation is highly likely.

"There is also the reputational risk of contributing to a global threat to human health which currently kills an estimated 700,000 people per year."

In response, the UK group 'Responsible Use if Medicines in Agriculture Alliance' (RUMA) said that farming is not solely to blame for growing resistance, and that considerable efforts are already being made to reduce antibiotic use.

The group said: “We recognise concerns about growing resistance to antibiotics, but in humans, resistance is largely attributed to human medical use with a recent study confirming farm animal use could be responsible for as few as one in every 370 clinical cases. Despite this, resistance is a threat in animals too and the farming industry, as well as those looking after the health of horses and pets, must ‘do its bit’ to control spread.

“The concept that food companies work sustainably with their supply chains to reduce the need for antibiotic use in farm animals is welcomed by RUMA; this is already happening.

"However, it’s critical that potential impacts on welfare, food safety, product quality and investment are fully understood by the businesses involved so that farmers have the confidence, means and support to make any necessary changes.

“It is equally important this issue does not end up being exploited as a marketing tool. There is a risk that misrepresentation of facts and a failure to appreciate the situation in different countries could end up harming welfare, cause unnecessary suffering and lead to significant losses in our farm livestock sector.

RUMA highlighted the differences between the countries on antibiotic regulation and said that failure to appreciate these differences could lead to "unnecessary suffering and significant losses".

“For example, while a reported 70 per cent of antibiotics in the US might be used to tackle disease challenges in farm animals, it’s only 40 per cent in the UK, with Public Health England figures showing medical use of antibiotics is actually 2.4 times that of veterinary, based on kg per biomass (i.e. when corrected for number and weight of animals and people).

"Furthermore, use of antibiotics as growth promoters has been banned in the EU since 2006; antibiotics are only available in the UK on prescription from vets; and the industry has already opted for restrictions to use a number of antibiotics classed as critically important for human health, such as 3rd and 4th generation cephalosporins, fluoroquinolones and colistin, only when truly necessary.”