Ofsted’s “deep dives” into the curriculum have focused on reading and mathematics, but reports show inspectors are scrutinising subjects outside their expertise.

Schools Week’s analysis of the 55 inspection reports published so far show they focused on maths in 50 schools and reading in 46.

However, some lead inspectors are not listed on the Ofsted website as having the relevant subject knowledge.

For example, David Selby led an inspection that covered reading, maths and history at Wray with Botton Endowed Primary School in Lancashire. His Ofsted pen portrait shows he has expertise in science.

Lucy English, who is listed as having expertise in English and maths, led an inspection of Lyminster Primary School in West Sussex that focused on maths, science, art and music.

Heather Phillips, who the Ofsted website says specialises in primary science, led an inspection at John Wheeldon Primary Academy, in Stafford where deep dives included English, reading and writing, maths and PE.

Ofsted research into its own inspection methods, published in June, showed inspectors without relevant subject knowledge were less reliable assessing curriculum, teaching methods and workbooks at secondary level.

Mary Bousted, the joint general secretary of the National Education Union, warned deep dives were “a lottery”, with many inspectors “simply unqualified” to examine the subjects.

Paul Whiteman, the general secretary of the National Association of Head Teachers, said predictions over “harmful inconsistencies” have proved “accurate”, adding Ofsted should be “open about any problems and work at a fast pace to put them right”.

But a spokesperson for Ofsted said “extensive curriculum training over the past two years” meant inspectors were “well equipped to make judgments about the quality of the curriculum without specialist knowledge of every subject”.