Traces of fecal bacteria have been found in drinks at three of the world's biggest fast-food chains in the United Kingdom.

An investigation has found that , and served ice in drinks contaminated by fecal matter. Investigators from the BBC consumer show "Watchdog" tested 10 samples at each of the chains and tested for traces of "fecal coliform," which carry a number of diseases.

Coliforms were found in three samples of McDonald's drinks, six of Burger King's and in seven samples taken at KFC sites. Four of the samples taken at Burger King and five at KFC were described as having "significant" levels.

In a response, reported widely by media, a KFC spokesman said: "We are shocked and extremely disappointed by these results."

"We have strict procedures for the management and handling of ice, including daily and weekly inspections and cleaning of the ice machine and storage holds, as well as the routine testing of ice quality across our business."

Burger King's response has also been widely circulated by media outlets: "Cleanliness and hygiene are a top priority for the Burger King brand."

"The strict procedures we have in place are designed to ensure all Guests have a positive experience each time they visit our restaurants," the Burger chain added.

Neither KFC or Burger King were immediately available for a response when contacted by CNBC.

A McDonald's spokesman told CNBC: "We have robust procedures in place with regard to the production, storage and handling of ice in our U.K. restaurants."

"Nothing is more important than the safety of our customers and people and we will continue to review our procedures and training, working closely with our restaurant teams to ensure those procedures are adhered to at all times," the spokesperson said.

McDonald's also cited comments from Tom Humphrey, professor of bacteriology and food safety:

"It is pleasing that Escherichia coli (E. coli), the bacterium that is the most accurate and reliable indicator of fecal contamination, was not found in any ice samples from McDonald's restaurants.

"Low levels of two other indicator bacteria, coliforms and enterococci, were found in some ice samples. These can be used as an assessment of water hygiene but, as they are widely distributed in the natural environment, they are not reliable indicators of potential health risks."

Find out more on the BBC's website here.