Schools are cutting back the curriculum and not replacing teachers when they leave because of a growing funding crisis, the chief inspector of schools has said.

In an unprecedented step, Ofsted’s Amanda Spielman laid out the impact of cuts in a blogpost that has since been removed because it was published “erroneously”. It will be published again in the coming weeks, along with a more detailed study on school funding.

Spielman has previously been criticised after she said it would be “inappropriate” for her to comment on issues on which Ofsted did not have “clear evidence”.

But in the blog, posted on Wednesday, she said since 2015 “costs have been rising more rapidly than income”, and accepted that cuts to local authority budgets have had a “significant impact”.

However, she was also critical of some schools’ responses, adding that “few school leaders carefully monitor the impacts of their responses to financial pressure”.

She said schools were responding to funding pressure by reducing curriculum breadth, with languages, computing, design and technology and music most affected.

She added that in some of the secondary schools the inspectorate visited subject specialists were not being replaced when they left and other teachers were teaching outside their specialism.

Stephen Rollett, a curriculum and inspection specialist at the Association of School and College Leaders, welcomed Spielman’s warning but said he was “disappointed that she accuses schools of failing to do enough”.

He said: “Let’s be clear that the blame lies with the government, which has caused the crisis by failing to fund schools properly and leaving them with no alternative other than to make cuts.”

Spielman said children with special educational needs faced the brunt of cuts, giving the example of one school where a specialist in this area was given a full teaching load.

“In another [school], teachers were asked to deal with SEND-S [special educational needs students] by differentiating instruction using a five-side registration sheet recording the needs of every pupil in the class,” she said.

The blog reads: “In some schools, experienced teachers were replaced with less-experienced and lower-qualified staff. Schools also reported cutting back continuous professional development and removing teaching and learning responsibility points.

“In some schools, higher-level teaching assistants were being used to cover classes when teachers were absent, rather than the school paying for teachers to cover these lessons.”

One passage reads: “In some cases, there was insufficient monitoring of the quality of education and support for the most vulnerable pupils, as we saw in the examples given above. This means that some schools are making the situation for pupils with SEND and their parents and carers harder and contributing to the fragmentation of local provision.

“Many schools we visited were narrowing their curriculum, to the detriment of the education of all pupils, especially those from the most disadvantaged backgrounds.”

Rollett said schools spend most of their budget on staffing so they did not have any option other than to reduce courses and extracurricular provision if they have to make cuts.

“It is the last thing they want to do but they have been left with impossible choices, and no amount of monitoring makes that situation any better,” he said.

The Department for Education said it would comment on Ofsted’s report when it was published in full. “This government has announced the biggest funding boost for schools in a decade, giving every school more money for every child,” a spokesperson said.

Rollett said: “The government has now pledged more money for schools, which is a welcome move, but it is not enough to reverse the cuts.”

The blog ended with Spielman saying that Ofsted will be carrying out research to see whether it is helpful for inspectors “to go into schools with some financial indicators”, but said it would need to make sure whatever they do is “does not add an unnecessary layer on top of existing financial accountability measures”.

Ofsted’s research, which is yet to be published, involved surveying 201 heads, and research visits to 16 schools. Senior leaders, school business managers, teachers, support staff, governors and trustees were all interviewed. The sample included eight primary and eight secondary schools across England.