Ealing Council received a complaint that mice were spotted in the school kitchens last year on what the school says was a staff training day on November 25.
The academy school's caterer, Olive Dining Ltd, was initially inspected on November 24 and given the top hygiene rating of five.
But now the school, which opened in 1930 and caters for pupils in Years 7 to 11, as well as a Sixth Form, has a zero rating after the council re-rated the canteen a day later, shortly after the complaint had been lodged.
However, following concerns, the council has since said it is "now satisfied that there is no risk to public health" and has removed its third-party inspectors from its contract.
A council spokesman said: "Olive Dining Ltd (the caterer at Drayton Manor High School) was subject to an unannounced inspection on 24 November by one of our third party contractors and was found to be satisfactory.
"However shortly afterwards, the council received a complaint that rodents had been seen in the school kitchens.
"A council inspector visited the school on the same day and the conditions and compliance with food safety controls on that day were judged to be unsatisfactory, resulting in the council re-rating the business.
"We are pleased to say that the business fully cooperated with the council to remedy the problem and we are now satisfied that there is no risk to public health.
"Having identified the discrepancies in standards between the two days, we immediately removed the third party inspector from our contract and took immediate steps to complete a re-inspection of the businesses they visited to ensure that our high standards are maintained.
"Olive Dining Ltd is due another inspection visit in six months.
"However, they can ask to be re-rated sooner by requesting an unannounced inspection. The business has yet to request this."
The school's headteacher, Sir Pritpal Singh, wrote to parents on Friday (February 3) about the rating, after discussions on social media he described as "not entirely accurate".
He told parents the school, which is rated "outstanding" by Ofsted, was given a food hygiene rating of five following the inspection on November 24, before it was downgraded the following the day.
Parents were told this came after the council had received a "complaint", but the letter does not give information on what the complaint was.
Sir Pritpal said the school had sought to be re-rated sooner than the estimated six months from the last inspection, despite the council's claim it has not yet received a request to do so.
The letter, which the school sent to getwestlondon for publication, reads: "I am writing to you with regard to the hygiene rating of the school's dining facilities.
"We are aware that there has been some discussions of this on social media, the content of which is not entirely accurate and we hope that this letter will allay any concerns you may have.
"On Thursday 24 November 2016, the school had a routine, unannounced Environmental Health officer visit from the local authority.
"The inspection went very well and the school was awarded the highest food hygiene rating of 5.
"On staff training day on Friday 25 November, Ealing Council received a complaint and downgraded the school.
"Remedial works were carried out immediately and over the weekend.
"Once the works were carried out, the environmental health officer returned on Monday 28 November.
"He was more than content with the works that had been completed and verified our compliance.
"Unfortunately, in accordance with standard practice, Environmental Health will not re-rate the food hygiene rating with a number until three months have passed.
"The school is unhappy about this because we want to give maximum assurance to students and their families.
"We are not a commercial supplier of meals. School meals are a public service and it is essential that parents are able to trust to the quality of provision because, unlike where a restaurant is concerned, students have no alternative.
"We believe this means that Ealing should be prepared to re-rate without delay, not for our benefit, but for that of those we serve.
"We have sought professional advice on the matter with a view to expediting the re-rating, however Ealing Council have confirmed that as per standard practice, they will carry out an unannounced inspection, three to six months after the re-rating on 25 November.
"In the meantime, we are confident that we comply with all obligations on us, and are comforted by the recent positive inspection by Ealing."
The council said a request to re-rate the canteen could have seen it re-inspected three months earlier than the estimated six months, from the date of the last inspection.
Are you a parent of a pupil at Drayton Manor High School? We'd like to hear from you! You can contact Ealing reporter David Rivers on 07 909 532 432 or email email@example.com.
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