A senior academic has claimed that the methods used by Ofsted inspectors in England for making their judgments about schools may not be reliable.

Professor Robert Coe, voiced a concern of many people in maths and English teacher jobs, namely that there was no proof the watchdog's lesson observations led to valid judgments.

The director of Durham University's Centre for Evaluation and Monitoring told a major educational research conference that Ofsted needs to show evidence that its techniques are valid and evidence-backed because millions of pounds are being spent in the hope that inspections can be a method to help raise educational standards.

Speaking to the BBC, Professor Coe pointed to some studies that suggested inspections are detrimental, with schools taking a long time to recover from negative inspections.

He said: "If you sit in a classroom, everyone thinks they can judge how good the lesson is - but can you really?

"Quite a lot of research says that you can't."

"Teachers are trying to do what Ofsted wants - but does it really make things better?"

Ofsted inspections could be affected by variables such as the charisma and confidence of the teacher, the subject matter being taught, students' behaviour in the classroom and the time of day, said the professor, who questioned how ratings could be consistent.

Sir Michael Wilshaw Ofsted's chief inspector responded by saying the claims were "tosh and nonsense".

He told the Times Educational Supplement that he is unaware of any head teacher who doesn't believe that classroom observation isn't anything other than an aid and highlighted Ofsted figures showing a nine percentage point rise in the proportion of schools judged good or outstanding as a way inspections had "galvanised the system".

As a teacher or someone looking for a teaching job, who do you think is right? Are inspections necessary? Are Ofsted conducting them in a thorough and fair way? Do they galvanise the system?