A teacher who was poisoned after a pupil poured whiteboard cleaning fluid into her drinking water has lost a compensation claim for Pounds 700,000 against her local authority.

Shaaira Alexis had her drink contaminated by a 15-year-old girl whom the teacher had previously called a “white prostitute” during a lesson, a High Court judgment found this week.

Ms Alexis, who taught at Brampton Manor School in Newham, east London, sued Newham council, claiming that the poisoning had ended her career and caused her long-term mental health problems.

The English teacher was treated in hospital after the incident but, although she recovered from the physical effects within a week, she did not return to school for five months because of anxiety attacks.

The court accepted her evidence that, after going back to work, Ms Alexis was initially terrified to leave her classroom. This led to her urinating in a bin.

But the poisoning also followed an incident in which Ms Alexis had called the girl responsible a “white prostitute” in front of other pupils.

Deputy judge Roger Ter Harr criticised Ms Alexis’s behaviour. “The significance of this cannot be understated,” his ruling said. “It is clear that in this multiracial school it was rightly quite out of the question for any teacher or student to be allowed to act or speak in a racist manner.”

Ms Alexis’s water had been poisoned after another teacher gave two pupils a key to her classroom while she was out of school.

While retrieving work from the room, one of the pupils poured the whiteboard cleaning fluid into a water bottle that Ms Alexis kept in her desk.

Ms Alexis told the court that having taken two or three mouthfuls from the bottle the following day, in February 2005, she felt an intense burning in her throat and felt she was choking.

But Mr Ter Haar denied that the local authority, as the employer of the teacher who gave the pupils the key, had failed in its duty of care.

The judge said it had been a serious incident that had caused “significant psychological consequences” for Ms Alexis. He also said that nothing in his judgment “condones the disgraceful behaviour of the pupil responsible”.

However, the judge said it would be “absurd” if teachers did not have the discretion to ask pupils to get something from another classroom. Staff could not have foreseen what happened, the ruling said.

The judge dismissed Ms Alexis’s claim that she would have been promoted to headship by 2012, saying it was doubtful that she would have continued as a secondary teacher at all because of stress. If he had found in her favour, Mr Ter Haar said, he would have awarded Ms Alexis Pounds 40,000.

The judge found that Ms Alexis had experienced culture shock after starting at Brampton Manor. Although an earlier evaluation had described her as an “excellent” teacher, Ms Alexis pointed to problems with the pupils, including an occasion when she was pelted with potatoes by a student while waiting at a bus stop.

The ruling said that was not typical of Brampton Manor, which was described as “good” by Ofsted after its most recent inspection.