A dental nurse of Indian-origin has gone on trial for allegedly attempting to poison her boss by spiking her coffee with mercury amalgam, used in dental fillings, after being pulled up for her “poor performance”.

Ravinder Kaur (34) is charged with administering “a poison or noxious substance with intent to injure, aggrieve or anno”. She denies the charge.

A court was told that the incident happened when her boss Laura Knowles called her to discuss her performance, three days after giving her a final written writing in March last year.

Ms. Kaur reportedly offered to make coffee for her but when Ms. Knowles drank it she did not like the taste. Within minutes, she started feeling sick with stomach cramps and was rushed to hospital, where X-ray revealed mercury fillings in her stomach.

The prosecutor, Samantha Cohen, told the jury: “This defendant put mercury amalgam into a cup of coffee she had made for her boss. Ms. Kaur did so out of spite and revenge because she believed she had been treated unfairly at work by her boss.”

Ms. Kaur started working at Shams Moopen Dental Practice in Shefford, Bedfordshire in November 2011.

Initially considered “meticulous and professional”, Ms. Knowles later “formed the view she was inflexible and not regarded as a good team player”. The jury was told that Ms. Kaur “flatly refused to work with one of the dentists” and on one occasion she left a patient in the chair saying she needed a lunch break.

She was given a final warning in March last year.

“Miss Kaur thought the warnings were unwarranted and unnecessary. She said she thought she was being set up by a member of staff because she had made a report to the authorities,” the prosecutor said.