A cyber attack on a school federation with sites across south east London left thousands of students unable to access their email.

Harris Federation, which has primary and secondary schools in Beckenham, Penge, Bexley, Orpington and Eltham, became aware of a ransomware attack on March 27.

Cyber criminals accessed the group’s IT systems and encrypted their contents.

As a precaution, the trust has temporarily disabled its email system and any devices given to pupils.

A spokesperson for Harris Federation said: “This is a highly sophisticated attack that will have significant impact on our academies, but it will take time to uncover the exact details of what has or has not happened, and to resolve.

“In addition to using the services of a specialised firm of cyber technology consultants, we are working closely with the National Crime Agency and the National Cyber Security Centre.”

The Government’s National Cyber Security Centre issued an alert about a spike in ransomware attacks affecting schools.

Harris Academy says it is at least the fourth multi-academy trust to have been targeted in March.

The trust has asked parents to temporarily avoid telephoning them or any Harris academy other than to report absence or emergencies.

Most Harris Federation schools will finish term tomorrow.