A grammar school pupil accused of sprinkling nuts on her allergic teacher's desk has been excluded despite passing a £600 lie detector test her father paid for.
Alexandra McDonald, 16, was suspended for 20 days alongside Maddie Colley, 17, after they were accused of targeting a teacher with a severe nut allergy at Rochester Grammar School in Kent.
Both pupils maintain their innocence and Alexandra's father, Peter McDonald, paid for a lie detector test that found she was telling the truth.
The two-hour polygraph test he hired claims to be 98 per cent accurate.
Mr McDonald, 64, said: 'The school said it was a serious health and safety offence and the teacher could have died.
'They said there was a witness who saw the girls giggling in the hallway close to the classroom during the time period they think it happened.
'The teacher apparently looked up because they heard the giggling - but that isn't evidence that they did it.
'The school said they excluded the girls based on the probability that they did it - there is no evidence. It's ridiculous.'
Alexandra says she was simply searching for her blazer with Maddie in a free period.
But teachers refused to believe her and she will now have to sit her A-level mock exams at a different school and in isolation.
Her outraged company director father decided to pay for a professional lie detector company to question his daughter.
'It was one of my friends who suggested Alex take a lie detector test,' the father-of-three said.
'I did a bit of research and found a reputable company. The woman who came around has been doing it all over the world for 15 years. It wasn't a Mickey Mouse one.
'She said the results were very precise and they are more accurate when tested on young people. There were three rounds altogether including practise questions and Alex passed all of them.
'A pad was put on the chair and there were blood pressure gauge, a strap that went across the chest and wires that connected to the fingers. They filmed the whole thing and we had to leave the room.
'Alex was asked questions which covered Maddie too - whether they did it and if they knew who did it.'
He said he and wife Sharon had to take Alexandra, who has a twin brother and older sister, to the doctor because of the stress caused by the accusation.
He added: 'She is usually bubbly but she has drawn into herself now and hardly leaves her room.
'We took her to the doctors because she is so stressed. She will be sitting her first A level mock exam at another school.
'We don't know if this accusation will have bigger consequences down the line.'
Alexandra's father is now demanding that the school overturns the 20-day exclusion that followed last week's incident.
'The exclusion will be appealed to the school governors, so I got the lie detector done to prove her innocence.
'I told the school about the lie detector and they weren't interested, it's so frustrating.'
Alexandra, who plans to study at the University of Kent to become a teacher, said 'I'm gutted.'
'When I was told I was going to be excluded I was shocked, I couldn't speak.
'I've always wanted to be a teacher but this makes me think it's not something I want to do, if this can happen to an innocent person. It definitely was not me.
'I loved school and the environment, I thought all the teachers were really friendly, understanding and there to help.'
People who are allergic to nuts can go into anaphylactic shock and in the most serious cases, their throats can swell and they can choke to death if they don't get urgent treatment.
Alexandra claims she was 'searching for her blazer' during a free period with Maddie when a teacher ordered them downstairs to another classroom.
On their return, they saw the crushed food on the floor but thought nothing of it as break time had just finished.
Maddie is preparing to sit mock exams in PE, geography and psychology.
Her mother Michelle Colley said: 'It's just really disappointing. It was Maddie's 17th birthday on her first day of being excluded so that put a dampener on things.
'We have tried to convince the school but they have made their decision based on probability and they won't listen to any other argument.
'I am hoping they will reconsider on the new evidence. I don't think we would go down the lie detector route but Maddie says she would take a test too.
'This will go on her permanent record if it doesn't get sorted. I fully believe her - if it was a practical joke she would have admitted it by now.
'I was actually very relieved when Peter told me he hired a lie detector test. I was really impressed, it's imaginative.'
But the girls-only school defended the decision, saying that parents are aware of a 'no nuts policy', which has been in place for 20 years.
A spokeswoman for the trust that runs the school said: 'Following an internal investigation, we took the decision to temporarily exclude two students for their part in an extremely dangerous incident that could have had fatal consequences.
'We make no apologies and are surprised a parent of one of the students does not see the seriousness of their actions and is contesting the decision to exclude.
'This is subject to the process on exclusion which is being followed in accordance with the guidance from the Department for Education.
'The school has been nut free for over 20 years, and information is sent to every parent on their child starting at the school to confirm this.
'In addition, students are reminded of this at the beginning of each academic year, and it is written in their starter booklets.'