A drink from Starbucks, Costa or Cafe Nero could contain traces of faecal bacteria, a study from the BBC has found.
BBC One's consumer series Watchdog tested for cleanliness on tables, trays, and high chairs at branches of the high street giants, while also collecting samples of the ice used in drinks.
Scientists found that the ice sometimes contain faecal coliforms at levels described as 'off the scale'.
The coliforms, which can cause illness and infection, were found in 7/10 samples from Costa, 3/10 samples from Starbucks and 3/10 samples from Cafe Nero.
As part of their investigation, the team consulted Tony Lewis - Head of Policy and Education at the Chartered Institute of Environmental Health on the findings.
Speaking within the programme, Tony said: "The level of contamination of faecal bacteria concerns me a great deal. The bacteria found are opportunistic pathogens – the source of human disease.
"These should not be present at any level – never mind the significant numbers found."
The coffee chains have responded to the investigation.
"We were disappointed with the findings, especially as these stores are all rated Very Good with a the top Hygiene Rating of 5.
"It is extremely important to us that all our stores operate to high standards of hygiene at all times and we take it very seriously when any store fails to meet these standards.
"We adopt industry standard cleaning processes across all our stores, in line with the Food Standard Agency's advice.
"Following these results we took immediate action to review our food safety procedures and have updated our ice handling guidelines and are in the process of introducing new ice equipment storage across our estate."
"We want to assure your viewers that we take hygiene and cleanliness extremely seriously.
"We have moved quickly to conduct our own investigation into the claims about the stores you have identified.
"All employees nationwide have received updated training on our high standards of hygiene including ice handling. Nothing is more important to us than the safety of our customers."
"At Caffè Nero we take the cleanliness and safety of our stores very seriously.
"We have a team dedicated solely to ensuring that all aspects of safety are maintained and our stores have detailed and timely cleaning schedules to ensure that they are kept up to standard.
"These standards are regularly audited by our Operations team.
"Our food safety standards and procedures are signed off by our Primary Authority Partner, Eastleigh Borough Council who also work with us to continuously improve our high standards.
"All of our staff are trained on these procedures and 99% of our stores are rated as very good, good or satisfactory by their local EHO – making us one of the most highly rated businesses on the high street.
"We are concerned to read the findings in your recent report and a thorough investigation is now underway and the appropriate action will be taken."