The cause of a norovirus outbreak that affected more than 250 peoplefollowing a Royal College of Art (RCA) graduation ceremony cannot be conclusively pinpointed.
Public Health England said norovirus had been picked up from a number of possible sources, but that no single origin could be identified.
The exact location where the event took place has not been revealed, although it has been confirmed that CH&Co was the caterer.
A spokesperson for CH&CO said: "We have learned that norovirus was the cause of the stomach sickness following the RCA graduation event but there is no direct evidence to show that there was anything wrong with the food.
"We have fully cooperated with the thorough investigation to identify the source of the problem, including liaising with our suppliers, however PHE has concluded that it is impossible to pinpoint the single source.
"Full reviews of our premises and procedures were found to be fully compliant and we had no employees affected by norovirus before the event. We will continue to emphasise to all employees about the important part they play in food hygiene and customer safety and this remains our priority."
Symptoms experienced by those who had fallen ill were described as "short and self-limiting" with no reports of long-term illness.