The schools will be known as Hasmonean High School for Boys and Hasmonean High School for Girls.
The division into two schools has been approved by the Department for Education, Mr McClusky said, but final implementation awaited completion of the relevant legal papers.
Although the school was officially a single institution, boys have been educated on a site in Hendon, while the girls study in Mill Hill.
But governors are still hoping to proceed with a redevelopment plan which would relocate the boys to a new building next to the girls.