An investigation is under way at a U.K. hospital after 10 staff who took part in a food trial were struck down with illness.

Eight of the catering team at Raigmore Hospital in Inverness received treatment in the accident and emergency department.

The workers were testing a new food product aimed at patients with swallowing difficulties, such as stroke victims and dementia sufferers.

Symptoms ranged from temporary loss of vision to facial inflammation. None of the staff was detained in hospital and all are now back at work. No patients were affected and the kitchens were not shut down. It is believed that the illness was not food-related, a spokeswoman for NHS Highland said. The food packaging is the suspected source of the illnesses.

A source, who wished to remain anonymous, said: "Some had lost their vision because their eyes were so swollen, they couldn’t open them. It must have been frightening."

"I am surprised the kitchen was not closed down for a while to find out what was going on," the source added.

Raigmore has 577 beds and employs around 3,200 staff. The catering department has 60 staff who provide 2,500 meals a day to patients, staff and visitors.