One of England's biggest academy chains has been condemned by Ofsted after inspectors found that eleven of its schools are failing to give children a good education.

In a damning letter to the E-ACT Trust, Ofsted warned that the chain had failed to take effective action to improve standards in many of its schools.

The schools watchdog had launched a series of inspections of the Trust's schools - visiting 16 of its academies in two weeks amid continuing concerns about under-performance.

Inspectors declared five of the academies inspected - including one new free school, Hartsbrook E-ACT free school in north London - to be failing and require special measures, while a further six were rated as "requires improvement".

Four were judged to be good and just one, Heartlands Academy in Birmingham, was found to be outstanding.

Ofsted said that ten of the academies inspected had failed to improve since their previous inspection, and of these, six had gained a worse Ofsted grade.

In its letter to E-ACT boss David Moran, Ofsted warned that "an overwhelming proportion of pupils attending the E-ACT academies inspected were not receiving a good education."

It added: "The evidence collected during these inspections indicates that intervention and support provided by E-ACT was ineffective overall. For those academies judged to require 'special measures', the Trust failed to take effective action to improve performance."

The letter, signed by Ofsted's regional director for the West Midlands, Lorna Fitzjohn, concluded: "There is an urgent need for E-ACT to take action to tackle underperformance in a relatively large number of academies in the Trust and to ensure that pupils' achievement rises to a good standard."