A local authority has been lambasted by Ofsted for a “downward trend” of “unacceptable” performance in its schools.

The withering attack on Northumberland County Council comes after the inspectorate swooped on 17 schools last month, as part of its move to target local authorities displaying consistent educational underperformance.

The findings appear to confirm that the watchdog had every reason to be concerned: four of the Northumberland schools inspected were placed in special measures - including one previously judged to be good - with a further nine placed in the “requires improvement” category.

Overall, three-quarters of the schools visited had declined or failed to improve their overall grade. Just one was graded outstanding.

A letter to the council from Nick Hudson, Ofsted’s regional director for the North East, Yorkshire & Humber region, reveals the extent of the inspectorate’s concerns.

“This downward trend of school performance is unacceptable against an overall national and regional improvement,” he wrote.

“Consequently, this means that children in Northumberland have less chance of going to a good school particularly in the middle and high school sectors. This result is unacceptable and will be of great concern to parents, carers and pupils alike.”

Traditionally, schools in Northumberland have performed above regional and national averages, the letter said, prompting “great concern” about the “significant and worrying decline in inspection outcomes” over the last 12 months.

The results of the most recent batch of inspections, Mr Hudson added, “do not reflect well on the local authority’s capacity or influence to drive improvement. The results suggest that the support provided by the local authority in those schools placed in special measures has not been effective, and it seems that actions to tackle weaknesses have not been swift enough to arrest the decline in these schools.”

Among Ofsted’s major areas of concern were the “inadequate” communication of its improvement strategy to schools, the “paucity” of its knowledge about pupils’ attainment and poor support for schools in dealing with underperforming staff.

Robert Arckless, the council’s policy board member for children’s services, said the council was taking the issues “very seriously and working hard to resolve” them.

“We will be working closely with the schools and increasing the levels of support so that together we can quickly improve the situation for the children and young people where it has been found to be inadequate,” he added.

“Although Ofsted found an improvement in some of the schools inspected and highlighted a range of strengths in Northumberland, we are now focused on making the tangible improvements required. We’re determined to get this right so that there is a good school for every Northumberland learner.”